Explore Cornwall's extraordinary geological past with the Cornwall Geologist.
Learn all about the dynamic story of Earth's history locked in the Cornish landscape and discover how it has shaped the landscape we see.

Cornwall Geologist is an Earth science educator and communicator, whose purpose is to promote, conserve, and educate about Cornwall’s fascinating geological history.

We provide guided walks and tours, talks and workshops, educational workshops and field trips, and consultancy services towards SW England geology and Earth Science education. Find out more about the services we provide below.

Come and explore Cornwall in a way you have never done before! Learn how to read the rocks beneath our feet to tell the story of our geological history, and discover how it has influenced Cornwall's environment, history, and culture.

About

Take a walk around Cornwall's world-class geological sites and areas of outstanding natural beauty whilst guided by the Cornwall Geologist!

Delve deeper in to Cornwall's geological past with talks and workshops hosted by Cornwall Geologist.

Develop and enhance your learning and teaching of geology and Earth sciences with the Cornwall Geologist.

With extensive knowledge and expertise, Cornwall Geologist can provide critical advice and practical solutions to the challenges you are facing.

Keep up with Cornwall Geologist's adventures and follow me on social media!

@cornwallgeologist

Geevor rainbow 🌈

Think there will more likely be a pot of tin at the end of this one though.

#geevortinmine #rainbow #cornwall #bbcweatherwatchers #lovecornwall

Multiple stages of mineralisation in a small vein system in granite atop Carn Eanes at Pendeen.

The outer black and white bands consist of quartz and tourmaline, with the inner bit being banded chalcedonic quartz with a vuggy centre and beautiful euhedral crystals growing inwards.

Hydrothermal mineralisation can occur in many geological settings across a range of temperatures and pressures. Aqueous fluids, known as volatiles, get heated up and mobilised.

If a rock fractures fluids can rush in to re-equilibrate the pressure, altering their ability to carry certain elements. Elements begin to bond together and precipitate minerals that fill the void to form a mineralised vein.

The chemical and thermodynamic diversity of hydrothermal fluids leads to a complex mineral paragenesis and distinct geospatial and temporal variations in mineralisation across Cornwall.

Repeated fracturing can create multiple episodes of veins. This, plus any alteration zones containing ore minerals is called a lode. They are often sub-vertical, up to several metres thick, and hundreds of metres in length and depth.

Most mineralisation in Cornwall formed as a consequence of the Permian granites.

Vast amounts of water is dissolved in granitic melt. As those magmas crystallise eventually those waters exsolve from the melt, known as magmatic-hydrothermal fluids.

This is likely what produced the original quartz-tourmaline veins here, forming at higher temperatures from a boron-rich magmatic-hydrothermal fluid.

Heat from the granite magmas also radiated through the host rock, mobilising connate and meteoric waters with different chemistries and causing them to circulate through the surrounding sedimentary and igneous rocks.

Long after the granite magmas cooled and crystallised they were still producing heat, originating from the decay of certain radioactive minerals.

This radiogenic heat mobilised salty brines in the sounding sedimentary basins during the Triassic, producing low-temperature, epithermal mineralisation locally known as crosscourse. This is likely the vuggy, chalcedonic quartz part of the vein system here.

#mineralisation #cornwall #geology #geologist #geologylife

A few doodles over some hidden structural geology gems in the foreshore platform at Jangye-ryn.

Low sand levels and late afternoon light illuminated this lovely first generation Variscan fold.

The fold is an asymmetrical anticline with an inclined axial surface dipping off to the SSE. The fold is facing and verging NNW.

The pale grey beds are composed of fine-medium greywacke sandstone and the dark grey is mudstone.

These rocks are part of the Portscatho Formation, forming in the Upper Devonian as submarine sediment gravity flows during syn-convergence sedimentation.

A strong cleavage has developed in the mudstone. Observing the relationship between bedding and cleavage orientation in inclined folds like these can help understand which bed is younging the right way up or if it is overturned.

If cleavage is dips steeper than bedding then bedding is the right way up. If bedding dips more steeply than cleavage then the bed has been overturned.

This is a really handy tool to understand large scale folding in areas with patchy outcrop and absence of any clear sedimentary structures to indicate way up and younging direction in sedimentary rocks. However, this only works with inclined folds where the cleavage is axial planar to the fold.

#structuralgeology #tectonics #variscan #cornwall #geology

Cornwall Geowalks coming up this February…

Cape Cornwall (half-day) - Monday 2nd February
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/cape-cornwall-guided-geowalk-half-day-monday-2nd-february-2026

Loe Bar (full-day) - Saturday 7th February
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/loe-bar-guided-geowalk-full-day-saturday-7th-february-2026

Tin Coast (half-day) - Saturday 14th February
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/tin-coast-guided-geowalk-half-day-saturday-14th-february-2026

Coverack (half-day) - Friday 20th February
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/coverack-guided-geowalk-half-day-friday-20th-february-2026

Bosigran (half-day) - Saturday 28th February
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/bosigran-guided-geowalk-half-day-saturday-28th-february-2026

Cornwall Geowalks are guided geology walks around Cornwall’s world-class geological sites and areas of outstanding natural beauty, guided by me! Please see the website for more details. Links in bio.

#geowalks #cornwall #cornwallgeology #geology #geologist

Whacking great alkali feldspar phenocrysts in a medium-grained, biotite-rich granite the Land’s End Granite at Wicca Pool.

These occur in a large granite sheet intruding the host rock immediately above the main body of granite below.

The biotite-rich granite could have resulted from differences in melt chemistry, evolving in situ or during transportation of the magma. It may also be from a different melt source from the other magmas.

Alkali feldspar phenocrysts occur in different quantities and sizes across the Cornubian Batholith.

Also called orthoclase or K-feldspar, they’re tabular in shape and possess a crystallographic property known as simple twinning.

A phenocryst is a mineral in an igneous rock that is larger than the groundmass. It’s a textural description and a rock containing phenocrysts can be called a porphyry (adj. porphyritic).

Their larger size could be due to having longer to grow, or if the magma they form in has the right ingredients/conditions to promote growth of that type of mineral.

The Al-rich nature of these granites makes them peraluminous, meaning the total aluminium content outweighs the total sodium + potassium + calcium content.

It’s now widely accepted that these phenocrysts formed from a crystallising melt. However, reasons for why they occur is still unclear.

It could be they were transported up from a deeper magma chamber. Their size and distribution could be controlled by volatile content in the magma. It could be down to mixing of different intrusions. Or all 3!

The laminar or sometimes more turbulent patterns in their orientation, likely due to magmatic flow during emplacement.

Still so much more to discover!

#granite #landsendgranite #swcoastpath #penwith #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #geologylife #geologyfieldtrip #zennor #minerals #biotite #wiccapool #cornishgranite

Finally, getting in on the aurora action. The northern lights from St Uny Church, 19/01/26.

I’ve seen them before, but only through a camera’s trickery. Not like this. It was incredible, humbling, emotional, magical.

I know these aren’t the best photos that will appear from this evening’s show, and most certainly not the only ones! But I’m just so pleased I’ve got to see them. I hope you did too, and it gave you all those amazing, positive feelings they did to me.

#northernlights #northernlightsphotos #northernlightscornwall #stunychurch #lelant #porthkidneybeach #aurora #auroraborealis #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #bbccornwall #amazingcornwall #stivesbay #cornwalllife #bbcweatherwatchers

This isn’t a fish skeleton fossilised in the Portscatho Formation at Dollar Cove near Gunwalloe. They are en echelon veins.

As well as being pretty, en echelon veins can tell us something about the sense of simple shear these rocks have undergone.

The veins form in tensile fractures within a shear zone, bounded by the upper and lower extents of the veins. For tensile veins to form there has to be extension perpendicular to their orientation, and shortening parallel to it.

Simple shear is when two planes slide past each other at the same distance but translate everything in between. Because the veins are continually being sheared after they form they begin to rotate around in the direction of shear, giving them their distinctive sigmoidal shape. All these examples here have a top sense of shear from right to left.

A bit hectic for Instagram, but I’ve drawn a strain ellipse on one image to show how this works. Pretty much, if you apply simple shear to something, there has to be a direction of maximum shortening and maximum extension within the object being sheared.

Increasing strain would cause the veins to continue to rotate round to 90° to the direction of shear. These shear zones can also sometimes develop a foliation that runs perpendicular to the veins and the maximum shortening direction.

All important bits of information in helping to understand how these rocks have been deformed during their history.

#echelon #enechelon #structuralgeology #shearzone #tectonic #tectonics #platetectonics #vein #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #geologyfieldtrip #geologylife #geoscience #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #gunwalloe #geologylife

I thought I’d provide you with a bit more information about the places we visit on our Geowalks. Next on the list - Coverack.

Taking a trip Coverack is also a journey deep inside the Earth! Here you can traverse the boundary between the Earth’s oceanic crust and mantle, discover the origins of the exotic rocks that make up the Lizard Peninsula, and learn of their journey to where we see them today on the Cornish coast.

The breadth of Cornish geology even includes its own ophiolite – a fragment of oceanic crust! Examine rocks that formed deep inside the Earth, and learn how at Coverack they tell us they formed at the Moho – the boundary between the Earth’s crust and mantle.

Discover of the origins of this rock that the Lizard is most famous for. Learn about the processes that gave us this popular ornamental stone, and its other uses as a source of industrial minerals.

Experience the impact of global tectonics that moulded the dynamic landscape around us. See where two mighty tectonic plates once collided, and learn how they dragged up rocks from deep inside the Earth.

#ophiolite #tectonic #coverack #lizardpeninsula #tectonics #geowalks #geotours #geologyeducation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #cornwallliving #visitcornwall #geologyfieldtrip #geologylife

I thought I’d provide you with a bit more information about the places we visit on our Geowalks. Next on the list - Lizard Point to Kynance Cove.

This walk along the coast at the southernmost point of Britain is also a journey through the exotic geology and landscapes of the Lizard Peninsula. Discover the origins of famous rocks like serpentinite, and explore the boundary where two tectonic plates once collided!

The breadth of Cornish geology even includes its own ophiolite – a fragment of oceanic crust! Get your hands on exotic rocks that formed in the Earth’s mantle, and learn about their dynamic journey to where we can see them on the Lizard.

Discover of the origins of this rock that the Lizard is most famous for. Learn about the processes that gave us this popular ornamental stone, and its other uses as a source of industrial minerals. You might also find the infamous soapstone used for making porcelain.

Lizard Point isn’t only a geographic landmark, but a geological one too. These are the oldest rocks in Cornwall, around 500 million years old! Discover these rocks that experienced extreme pressures and temperatures on their journey to where we see them today.

Experience the impact of global tectonics that moulded the dynamic landscape around us. See where two mighty tectonic plates once collided, and learn how they dragged up rocks from deep inside the Earth.

#lizardpoint #tectonic #kynancecove #igneous #tectonics #geowalks #geotours #geologyeducation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #cornwallliving #visitcornwall #geologyfieldtrip #geologylife

I thought I’d provide you with a bit more information about the places we visit on our Geowalks. Next on the list - Loe Bar.

Here we traverse the spectacular coastline around Loe Bar and Porthleven in south Cornwall, and explore Cornwall’s dynamic geological story of plate tectonics. Discover amazing structures in the rock, and learn how they tell us about when Cornwall was once at the centre of a giant mountain range.

Experience the impact of global tectonics that moulded the dynamic Cornish landscape around us. Discover structures in the rocks and learn how the shape of the land gives up its secrets for changing tectonics through time.

Discover the changing climate through Cornwall’s recent geological history, how this has shaped the landscape today, and what we can learn about how this may impact the county’s future.

Witness where the unstoppable power of the ocean does battle with the seemingly immovable Cornish coast at this famous location for watching storm waves. Learn how this hard rock coastline is being eroded, and what is being done to manage it.

#loebar #tectonic #structuralgeology #porthleven #tectonics #geowalks #geotours #geologyeducation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #cornwallliving #visitcornwall #geologyfieldtrip #geologylife

I thought I’d provide you with a bit more information about the places we visit on our Geowalks. Next on the list - Praa Sands and Rinsey.

Here we wander along this stunning coastline, exploring an array of amazing geological stories! Discover the origins of Cornwall’s most famous rock – granite, learn how the geological record tells us of a dynamic climate, and witness our relationship with an ever-evolving landscape.

Discover the origins of Cornwall’s most famous rock – granite. Get your hands on this amazing rock and learn how to identify the minerals and structures within, and see how their evolution gave Cornwall such mineral riches.

Discover a changing climate through Cornwall’s recent geological history, how this has shaped the landscape today, and what we can learn about how this may impact our future.

Explore the engineering prowess of Cornish miners, and how techniques they pioneered revolutionised global industry. See iconic engine houses that powered mining deep out under the sea.

Witness where the unstoppable power of the ocean does battle with the seemingly immovable Cornish coast. Learn how this hard rock coastline is being eroded, and what is being done to manage it.

#praasands #tectonic #rinsey #climatechange #granite #geowalks #geotours #geologyeducation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #cornwallliving #visitcornwall #geologyfieldtrip #geologylife

I thought I’d provide you with a bit more information about the places we visit on our Geowalks. Next on the list, my hometown - St Ives.

Here we explore the spectacular coastline and historic streets of St Ives. Learn about some of Cornwall’s dynamic geological stories, and discover how the foundation and history of the town owes its roots to the rocks that lie beneath.

Experience the impact of global tectonics that moulded the dynamic Cornish landscape around us. Discover structures in the rocks and learn how the shape of the land gives up its secrets for changing tectonics through time.

Discover the changing climate through Cornwall’s recent geological history, how this has shaped the landscape of St Ives today, and what we can learn about how this may impact the town’s future.

Explore St Ives and how the geology has influenced the town’s history and evolving industries such as fishing and mining. Discover what creates that unique light that draws artists to the area in their droves, and makes St Ives one of the country’s prime tourist destinations today.

#stives #tectonic #stivescornwall #stivesbay #granite #geowalks #geotours #geologyeducation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #cornwallliving #visitcornwall #geologyfieldtrip #geologylife

Massive quartz-tourmaline rock in the Land’s End Granite, at Porth Ledden near Cape Cornwall.

Massive quartz-tourmaline rock (MQT) contains <90% quartz + tourmaline. This can vary in individual bodies, and some show gradational changes to tourmaline granite.

They can have trace amounts of feldspar and mica, and may include accessory minerals apatite, zircon, monazite, rutile, ore minerals, and many more!

They occur as large mappable units, isolated pods and sheets and are spatially associated with tourmaline granites, typically with lobate contacts between them.

They range in grainsize. Some contain primary alkali feldspar phenocrysts that are variably pseudomorphed by quartz or tourmaline. Quartz can have zoned euhedral quartz overgrowths in places. Vugs (holes) are common. They often contain pods of 100% tourmaline or quartz.

The main question with this rock’s formation is did if form from a super-evolved melt or from hydrothermal processes.

The nature of MQT towards the apical parts of intrusions may suggest both. Mineralogical and textural evidence leads me to believe it is predominantly hydrothermal.

Amalgamation of volatiles towards the roof of an intrusion causes the selective dissolution and replacement of minerals by hydrothermal alteration within a crystal mush.

Not enough space to explain in full, but you can find more detailed data and discussion in published papers on this rock type. Head over to Google Scholar for a search. There is also a virtual microscope of this MQT’s cousin up at Roche Rock!

Regardless of the complicated science, it is a beautiful rock and definitely one of my favourites.

#granite #landsendgranite #penwith #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #geologylife #geologyfieldtrip #minerals #capecornwall #tourmaline #quartz #porthledden #kenidjack #geoscience

I thought I’d provide you with a bit more information about the places we visit on our Geowalks. Next on the list - Cape Cornwall.

Here we explore the incredible landscape around Cape Cornwall in the far west of Cornwall. It is the perfect place to experience some of Cornwall’s dynamic geological stories, producing one of the region’s most important industries – mining.

Discover the origins of Cornwall’s most famous rock – granite. You will get your hands on this amazing rock and learn how to identify the minerals and structures within, and discover how tectonic processes influenced their formation.

Learn about the unique geological processes that naturally enrich metals like tin and copper in the Earth’s crust, and how these natural phenomena gave Cornwall such rich mineral deposits. Get your hands on some rocks and minerals, and learn how to identify them.

Explore the engineering prowess of Cornish miners, and how techniques they pioneered revolutionised global industry. Discover the environmental and socioeconomic consequences of historic mining, how it impacts Cornwall’s landscape and culture, and how it may influence the region’s future.

#capecornwall #tectonic #cornishmining #penwith #granite #geowalks #geotours #geologyeducation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #cornwallliving #visitcornwall #geologyfieldtrip #geologylife

I thought I’d provide you with a bit more information about the places we visit on our Geowalks. Next on the list - Bosigran and Carn Galver.

Here we wander across the ancient land of west Cornwall, particularly the area around Bosigran and Carn Galver. This place is steeped in history, arching back to the Bronze age and possibly older. We will dig even deeper below the surface for an insight into Cornwall’s turbulent geological past.

Discover the origins of Cornwall’s most famous rock – granite. You will get your hands on this amazing rock and learn how to identify the minerals and structures within, and discover how tectonic processes influenced their formation.

Learn about the unique geological processes that naturally enrich metals like tin and copper in the Earth’s crust, and how these natural phenomena gave Cornwall such rich mineral deposits. Get your hands on some rocks and minerals, and learn how to identify them.

Experience the impact of global tectonics that moulded the dynamic Cornish landscape around us. Discover structures in the rocks and learn how the shape of the land gives up its secrets for changing tectonics through time.

Explore the local history and archaeology of this ancient land, and how the geology beneath has influenced human interaction with the landscape and the unique culture and folklore of west Cornwall.

#bosigran #carngalver #cornishmining #penwith #granite #geowalks #geotours #geologyeducation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #cornwallliving #visitcornwall #geologyfieldtrip #geologylife

I thought I’d provide you with a bit more information about the places we visit on our Geowalks. First on the list - the Tin Coast.

Here we venture along the coast around Botallack in the far west of Cornwall, known as the “Tin Coast”. It is the perfect place to experience how Cornwall’s geological past had its biggest influence on the landscape we see – mining.

Learn about the unique geological processes that naturally enrich metals like tin and copper in the Earth’s crust, and how these natural phenomena gave Cornwall such rich mineral deposits. Get your hands on some rocks and minerals, and learn how to identify them.

Explore the engineering prowess of Cornish miners, and how techniques they pioneered revolutionised global industry. Experience the iconic Crowns engine houses that powered mining deep out under the sea, and the remains of surface processing works for extracting metals from the rock.

Discover the environmental and socioeconomic consequences of historic mining, how it impacts Cornwall’s landscape and culture, and how it may influence the region’s future.

Enjoy a walk around the beautiful Cornish coast and countryside, taking in the stunning views and wildlife whilst experiencing this landscape from a new perspective!

#botallack #tincoast #cornishmining #mining #minerals #geowalks #geotours #geologyeducation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #cornwallliving #visitcornwall #geologyfieldtrip #geologylife

Cornwall Geowalks coming up this January…

Tin Coast (half-day) - Friday 16th January
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/tin-coast-guided-geowalk-half-day-friday-16th-january-2026

Praa Sands (half-day) - Monday 19th January
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/praa-sands-guided-geowalk-half-day-monday-19th-january-2026

Lizard and Kynance (full-day) - Saturday 24th January
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/lizard-point-and-kynance-cove-guided-geowalk-full-day-saturday-24th-january-2026

St Ives (half-day) - Saturday 31st January
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/st-ives-guided-geowalk-half-day-saturday-31st-january-2026

Cornwall Geowalks are guided geology walks around Cornwall’s world-class geological sites and areas of outstanding natural beauty, guided by me! Please see the website for more details. Links in bio.

#geowalks #geotalks #learninggeology #geotours #education #geologyeducation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #cornwallliving #visitcornwall #geologyfieldtrip #geologylife

Second phase deformation in rocks at Carne Beach on the Roseland.

Tectonics are continuous but their dynamics can evolve over time. Changes in direction and intensity of stresses in the crust deform rocks differently, which provide a record of how plate tectonics evolve through Earth’s history.

Here, a moderately inclined S2 crenulation cleavage and F2 folds deforms a bedding-parallel S1 cleavage.

We can tell the relative age from cross-cutting relationships. The S1 foliation has been buckled by strain that created the S2 cleavage.

Also, the earlier cleavage and bedding has undergone pressure dissolution along the S2 cleavage, making it look like layers have been cut out.

Both 1st and 2nd phase deformation in south Cornwall formed during convergence tectonics related to the Variscan Orogeny during the Paleozoic.

Both deformation events have a top sense of shear to the NNW. However, the relationships we see here suggest a time gap between events. There is also a clear change in strain intensity, with D1 being higher strain than D2.

Whilst D1 is ubiquitous in the area (another indication of high strain), D2 structures are more localised. They largely occur around late stage thrust faults, where strain is more likely accommodated.

The fact there are two distinct deformation episodes suggests this transition was not entirely progressive, and that there could have been a hiatus in Variscan tectonics.

One theory is it represents a change from subduction tectonics to continent-continent collision during the Carboniferous, after the two tectonic plates had effectively locked together.

#structuralgeology #tectonic #variscan #roseland #cornwall #cornwallgeology #cornishgeology #geology #geologylife

A fine-grained felsic igneous enclave in coarse grained Land’s End Granite down at Pellitras Point near Land’s End.

Limpets for scale - they’re around 1-2 cm in diameter.

An enclave refers to a piece of rock enclosed within an igneous rock. They can either be igneous enclaves, of which they could be mafic or felsic (like here) in composition. Alternatively, they can be non-igneous enclaves (metamorphosed sedimentary rocks).

The rounded, lobate contact of this enclave tells us the two igneous rocks must have coexisted as magmas. This is known as magma mingling. Think lava lamp, or oil and water. If an enclave has more angular contacts then it was probably more solid to break in a brittle manner.

Enclaves can be cm sized, and some hundreds of metres across. They can originate from two settings. One is where a magma body picks up fragments of other rocks or magma when being transported. Alternatively, later intrusions can get injected in to older bodies of magma when still predominantly liquid.

They mingle rather than mix because of a whole host of physical and chemical reasons. However, this is still likely to be some level of diffusion or trading of elements and minerals at the boundaries.

Some of the larger minerals inside the enclave could have been enveloped into it from the surrounding magma, like kneading currents in to dough. Sometimes they crosscut the contact. This is known as a protrusive contact.

Other names include xenoliths and schlieren, but these have more specific meanings. The former typically refers to metamorphosed host rock, and the latter is likely fragments of melt source rocks that have been mostly recrystallised.

#landsend #enclave #xenolith #granite #igneous #landsendgranite #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #geologyfieldtrip #geologylife #amazingcornwall #magma #lavalamp #cornishgranite #pellitraspoint

Happy New Year to you all! 🥳

Whilst today is just another day in the life, it does provoke reflection on what has been and thoughts as to what might happen next.

I do enjoy looking back through memories logged in this weird, virtual world. From the wonders of Cornwall’s geology and landscapes, to exploring new places.

So here is my Instagram top nine for 2025! And what a year it has been.

This year I launched Cornwall Geologist. Whilst it’s been a huge learning curve with many ups and downs, I am super proud of what it has achieved and look forward to continue building it in 2026.

This year I also started working at Geevor Tin Mine. As a kid visiting this place, it was instrumental in grabbing my interest in geology and mining at a young age, so to now say I work here all these years later is a very proud moment.

But the biggest and most proudest thing by far, not just this year but for all the years, is the arrival of our daughter! Eleanor Joy (aka Pebble) is now cracking on 3 months, and I’m so excited to see what 2026 brings as a dad.

I hope you all see out the year in peace and happiness with your loved ones, and I wish you all the best for your endeavours in 2026.

If you’re of the geology persuasion then keep up the good work learning and teaching about how our little blue planet works 🌍

#happynewyear #2025 #happynewyear2026 #bestnine #bestnine2025 #cornwall #cornwallgeology #cornishgeology #cornwallcoast #cornishcoast #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #walkingcornwall #explorecornwall #lovecornwall #structuralgeology #newyear #ukcoast #geologylife #geologyfieldtrip #instagramtop9 #coastalliving #swcoastpath

Geology so good one just has to take a photo! 📸

I bet you know the location …

#folding #deformation #structuralgeology #tectonic #tectonics #tectonicplates #variscan #variscanorogeny #crackingtonformation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #ordnancesurvey #getoutside #bbccornwall #geologylife

A lovely Boxing Day amble along Woolacombe beach to Mill Rock and back.

Beautiful winter sunshine illuminating the Upper Devonian Morte Slate Formation that crops out at Mill Rock. @jennawitts.music and Pebble for scale.

#woolacombe #woolacombebeach #woolacombebay #northdevon #northdevoncoast #devon #devoncoast #devonlife #devongeology #mortepoint #morteslate #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #devonscenery #ukcoast #ordnancesurvey #getoutside #bbcspotlight #baggypoint #devonian #coastalliving #coastmaguk #exploredevon

Happy Christmas to all! Have a fab day eating, drinking, being merry, and rockin’ around the Christmas tree!

Here’s a geo-themed festive photo of a snow-covered granite tor atop Rosewall Hill.

#cornishsnow #granite #granitetor #tor #rosewallhill #stives #penwith #landsendgranite #stivescornwall #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #cornwallphotography #christmasday #christmas

On the train heading up to North Devon for Christmas, which includes one of my favourite train journeys combining love of geology with trains - Dawlish.

The railway runs precariously between the sea and the bright red cliffs, famously doing battle (and losing) with coastal erosion.

It is stunning though, and the geology of these cliffs is spectacular.

They are made of rocks collectively known as the New Red Sandstone - Permo-Triassic sedimentary rocks that formed in an arid, mountainous environment around 250 million years ago.

The preceding Variscan Mountains were eroding away, shedding vast quantities of sediment down through canyons, alluvial fans, and braided river systems.

Surrounding these river systems were flood plains, and dune systems developed, evolved and migrated.

There are several sections in the cliffs where you can see the sweeping crossbedding that would have formed from windblown sand migrating across the desert in huge dune systems.

The bright red colour comes from iron oxide, or rust, that coats the sediment grains and cements them together. This is typical in hot, arid climates that promotes oxidation of iron-rich minerals like haematite.

The railway was constructed in 1844 as part of Brunel’s Great Western Railway. Whilst it is a beautiful stretch of railway it is incredibly vulnerable to coastal erosion and is constantly undergoing engineering work.

In the famous 2014 storms the sea wall was breached and a section of the railway was washed away, effectively cutting off Cornwall from the mainline. A £35 million repair project saw the line reopen in just 8 weeks.

#dawlish #dawlishbeach #dawlishwarren #greatwesternrailway #brunel #sandstone #triassic #desert #sanddune #sedimentary #sedimentaryrock #sedimentology #devon #devoncoast #southdevon #walkingdevon #exploredevon #lovedevon #devongeology #ukcoast #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #geologylife

Happy Winter Solstice to all! Summer is coming!

Looking forward to longer days and lighter evenings in 2026 and lots of exciting Geowalks!

#solstice #wintersolstice #summeriscoming #botallack #botallackmine #cornishmining #cornishmines #geowalk #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #ukcoast #swcoastpath #geologylife #geologyfieldtrip

A dig back through the PhD archive here, trying to decipher the complex magmatic evolution of the Land’s End Granite at Wicca Pool.

The coarse-grained, porphyritic biotite granite on the left is juxtaposed with a more medium-grained, biotite-rich granite with larger alkali feldspar phenocrysts.

These occur in a large granite sheet intruding the host rock immediately above the main body of granite below.

It is unclear whether these are separate intrusive events, or occur from in situ differentiation. Given the sharp contacts, it is more likely to be the former, but with no clear cross-cutting relationships it is difficult to tell which came first.

The more biotite-rich granite could have resulted from differences in melt chemistry, evolving in situ or during transportation of the magma. It may also be from a different melt source from the other magmas.

As you can tell, a PhD project can more often kick up more questions than answers! There is so much more to discover!

#granite #landsendgranite #swcoastpath #penwith #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #geologylife #geologyfieldtrip #zennor #minerals #biotite #wiccapool #cornishgranite

Folded flysch in North Cornwall.

Flysch is the traditional term for a broadly fining upwards sequence of sandstones and mudstones, deposited from turbidity currents (underwater avalanches) on submarine continental slopes.

The Bude Formation formed during syn-convergence sedimentation in the Culm Basin, and then subsequently buried and then inverted during the Variscan Orogeny. These rocks host some incredible sedimentary structures.

The Variscan folds here face southwards. Fold facing is the direction in which the beds get younger in the hinge of the fold. In this image it is left to right.

The southwards facing folds in this area are anomalous, contradicting the northwards transport direction of Variscan tectonics.

They occur because of the pre-Variscan faults that underly these units and controlled the formation of the Culm Basin. These faults towards the south end of the basin dip northwards. This dictated how strain was accommodated during inversion or the basin, with the expulsion of these sedimentary layers southwards.

The cliff height here is about 30 m.

#budeformation #flysch #widemouth #widemouthbay #cornwall #cornwallcoast #cornishcoast #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #explorecornwall #walkingcornwall #lovecornwall #bbcspotlight #ordnancesurvey #structuralgeology #sedimentary #variscan #geologyfieldtrip #tectonic #tectonics #tectonicplates

Quite an evocative image of the tunnel leading from the Miner’s Dry to the shaftbank at Geevor Mine in the setting sun.

The Dry at Geevor is one of the most interesting and poignant places to visit. It is a time capsule - left as it was from the day the mine closed in February 1990.

The Dry is the name given to the miners’ changing rooms. The name comes from the period when hot pipes from the steam engines provided a place where miners could dry the clothes they wore underground. Before this miners would have to walk home in their wet clothes, possibly several miles.

This is the place the miners would get to work and clock in at the start of the day and change in to their work clothes. They would receive instructions from shift bosses about their daily tasks, and collected equipment and explosives.

After that it would be down the tunnel to the landing house to wait for the cage down to the level they were working on underground.

At the end of the day it would be back up the tunnel to the Dry. They would shower and change back into their civvies. It would have been a noisy place, full of laughter, banter, and probably the odd heated debate (all with very blue language I’m sure!).

It’s deathly silent now, and quite eerie when locking up in the dark evenings this time of year.

The Dry at Geevor is the greatest tribute to those miners. Spending time here is the best place to get a feel what it would have been like, and gain respect for miners past and present.

@geevor_museum

#geevor #geevortinmine #geevortinminemuseum #tinmine #cornishmining #cornishmines #penwith #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #mining #visitcornwall #geologylife #geologyfieldtrip #cornwalllife

Hot stuff ☢️

Cornwall is famous for metal mining. We all know about tin and copper, but did you know several thousand tonnes of uranium has also been mined?

The principal mineral is called pitchblende or uraninite, a heavy, black, uranium oxide.

There are also secondary uranium minerals such as torbernite, autunite, and schröckingerite.

The green mineral here is torbernite, and the rather inconspicuous black rock is pitchblende. As you can tell from the dosimeter, the latter is particularly radioactive!

Famous locations where radioactive minerals have been historically mined include South Terras near St Austell, Wheal Edward near Botallack, and Trenwith in St Ives. The latter is right opposite where I went to school!

Marie Curie reputedly sourced some of her uranium samples from South Terras and Trenwith, from which she first isolated radium.

Most uranium extraction in Cornwall derives from reworking old dumps, where previously extracted material had gone to waste. Thankfully, this means there isn’t much left in the dumps.

This mining method has been common in Cornwall even to the present day, as advancing technologies see products previously considered waste become economically important.

Uranium minerals occur in veins, most likely late-stage epithermal mineralisation. Several stages of hydrothermal circulation has concentrated and reprecipitated uranium from older vein systems or where it occurs in the granites or sedimentary rocks.

It goes without saying that it is not recommended to collect and store these minerals. Whilst limited exposure is okay, keeping them in a shoebox in your office is likely to give you more than your recommended daily limit of radiation.

Whilst not the best things to keep, they’re still very pretty and interesting!

#uranium #pitchblende #radioactive #torbernite #radiation #minerals #hotrocks #stives #stivescornwall #southterrasmine #trenwith #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #geologylife #geologyfieldtrip

This strange looking photo is actually a rock! They’re called kernel structures that form in serpentinised peridotite. This is in a boulder down at Porthallow on the Lizard Peninsula.

Peridotites are ultramafic rocks that form in the Earth’s mantle. They’re mineralogy is predominantly olivine and pyroxene which are unstable, and their dynamic geological journey means they readily undergoes retrograde metamorphism and hydrous alteration known as serpentinisation. This is when the olivine and pyroxene alter to serpentine minerals.

Serpentinite (a rock full of serpentine minerals) got its name because its surface appearance looks like the skin of a reptile. The beautiful green serpentine polymorph mineral called lizardite does resemble the scaly skin of an actual lizard.

It is just a coincidence that the Lizard peninsula in south Cornwall is mostly made up of rocks that look like a serpent. The name Lizard is actually the anglicised name for the Cornish Lys-ardh, which, when translated, possibly means “high court”. The mineral lizardite is named after the Lizard peninsula though, after where it was first described. So the etymology is interwoven in some way!

If peridotite fractures then serpentinisation can occur along those cracks. These are called kernel structures. The first photo is actually where the rock has broken away along one of these fractures, exposing this beautiful texture. The second photo shows how they look in situ.

The peridotites on the Lizard are part of an ophiolite complex which is a fragment of oceanic crust that formed in the Devonian and was obducted on to the top of a continent during Variscan mountain building in the Carboniferous.

#peridotite #serpentine #serpentinite #mantle #lizard #lizardpeninsula #porthallow #variscan #ophiolite #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #geologylife #geologyfieldtrip #igneous #ultramafic

If you’re a structural geologist you’d get as excited as I do when you see fold hinges exposed like this, as it is just so much easier to measure them!

These beauties are F2 folds in the Portscatho Formation at Loe Bar.

We use the term hinge for a fold where the two limbs of the fold meet; where the bedding surface has bent if you like.

Think of it like the hinge of a door or the spine of a book. We would measure the compass orientation of this and its vertical angle relative to horizontal.

This way we can analyse the shape, movement and stresses they formed under, and make comparisons to other data from across the region.

This is classified as F2 because it’s a second generation fold. There was an earlier deformation episode preserved in these rocks that elsewhere have been deformed by this episode.

They formed during the Variscan Orogeny over 300 million years ago when two continents collided.

#folding #structuralgeology #loebar #porthleven #portscathoformation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #geoscience #amazingcornwall #geosciences #geologylife #geologyfieldtrip #variscan #cornwallnature #ukcoast

Had a fab Geowalk to Bosigran and Carn Galver, blessed with a brief window of late autumn sunshine!

Carn Galver engine houses were looking resplendent in the morning sun.

Carn Galver Mine was worked during the 19th Century, either independently or as part of Morvah and Zennor United Mines.

Production was intermittent, and limited output records 150 tonnes of black tin extracted in the second half of the 19th Century.

The two engine houses at the side of the road were built during the last attempt at working the mine in 1871.

The left hand structure housed a 30” pumping engine, and structure to the right just behind contained a 22” winding engine. The shaft used by the pumping engine reached a depth of 240 m.

The building just out of shot to the north of the engine houses was the mine’s count house, now used by the Climbers’ Club.

Rivers running down adjacent valleys to Porthmoina Cove and the neighbouring Porthmeor Cove were utilised for their water power to process the mined rock – to crush it down and separate out the heavy tin ore from the gangue (waste) minerals.

#carngalver #bosigran #carngalvermine #tincoast #geologyfieldtrip #granite #landsendgranite #enginehouse #cornishmining #ordnancesurvey #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #penwith #swcoastpath #geologylife

The 7 ft Hardinge Ball Mill at Geevor Tin Mine.

This machine is getting on 90 years old, but amazingly it still works! It’s amazing to see, although a lot quieter than it would have been when it was in operation.

Here’s some information from Geevor as to what its purpose was:

“The cassiterite occurred as very small grains within the ore. Finely grinding the ore liberated these grains from the enveloping rock and other minerals.

“The traditional method of grinding ore was to use stamps’ (a mechanical mortar and pestle). At Geevor there were originally eight Holman pneumatic stamps.

“During the early 1930’s small Hardinge ball mills were introduced to further grind the ore and improve cassiterite recovery. In 1937 the stamps were replaced by the present, more efficient, 7ft x 36in Hardinge conical ball mill.

“Ball mills work by tumbling the ore with heavy steel balls. As the mill rotated the balls broke down the ore by pressure, friction and impact.

“A flow of water washed the ore into the mill via the hollow feed trunnion, where it was ground to sand. The sand sized product passed out of the mill via the discharge trunnion to a screen (sieve).

“Any particles of sand which were still too large went back to the mill for further grinding. In this way the size of the ore particles could be controlled.”

A larger, 2.2 m-diameter Newell Dunsford Mill was later installed to increase capacity of the Mill at Geevor. Unfortunately, this was sold when the mine closed to a lead-zinc mine in Ireland.

@geevor_museum

#geevor #geevortinmine #geevortinminemuseum #tinmine #cornishmining #cornishmines #penwith #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #mining #visitcornwall #geologylife #geologyfieldtrip #cornwalllife

Cornwall Geowalks coming up this December…

Cape Cornwall (half-day) - Monday 1st December
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/cape-cornwall-guided-geowalk-half-day-monday-1st-december-2025

Coverack (half-day) - Friday 5th December
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/coverack-guided-geowalk-half-day-friday-5th-december-2025

St Ives (half-day) - Monday 8th December
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/st-ives-guided-geowalk-half-day-monday-8th-december-2025

Tin Coast (half-day) - Monday 15th December
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/tin-coast-guided-geowalk-half-day-monday-15th-december-2025

Cornwall Geowalks are guided geology walks around Cornwall’s world-class geological sites and areas of outstanding natural beauty, guided by me! Please see the website for more details. Links in bio.

#geowalks #geotalks #learninggeology #geotours #education #geologyeducation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #cornwallliving #visitcornwall #geologyfieldtrip #geologylife

The structural geology and sedimentology along the coast at Godrevy is epic.

Here are some stunning folds in the cliffs just north of Godrevy Cove.

These structures have previously been interpreted as back folding associated with 2nd generation, northwards verging Variscan convergence. They were collectively part of what was coined the Godrevy Antiform.

Subsequent work has reinterpreted them as forming during the later 3rd phase of deformation, associated with regional extension after mountain building had ceased.

Their geometry and kinematics are incompatible with D2 and more akin to D3, and further down the beach you can see these structures crosscut D2 structures.

This lithostratigraphical unit is the Porthtowan Formation. It comprises interbedded mudstones and sandstones, and is variably folded, faulted, and cross-cut by quartz veins.

The unit formed in the Devonian, 370 million years ago, being deposited in an ocean setting on the flanks of a continental shelf, where it slopes down to the abyssal plain.

These rocks were subsequently buried and then deformed during Variscan mountain building in the Carboniferous, and then during subsequent extensional tectonic deformation in the Permian, all of which is described above.

#folding #structuralgeology #tectonic #tectonics #tectonicplates #godrevy #godrevybeach #godrevypoint #stivesbay #cornwall #cornwallcoast #cornishcoast #cornwallgeology #cornishgeology #lovecornwall #explorecornwall #walkingcornwall #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #radiocornwall #porthtowanformation #geologylife #geologyfieldtrip

Reminiscing about our amazing trip to Scotland last year, especially visiting this place.

This is the incredible exposure of the Lewisian Complex in a road cutting just north of Laxford Bridge - some of the oldest rocks in Britain.

This road cutting beautifully displays the long and complex history of the Lewisian. Detail can be missed where it has a dull weathered crust, so these fresh exposures are a geologist’s dream!

The Lewisian Complex is part of the North Atlantic Craton and consists of high-grade metamorphic basement rocks. It crops out across the Outer Hebrides and the NW of Scotland.

It is also called the Lewisian Gneiss (pronounced “nice”). Gneiss is a coarse-grained, banded metamorphic rock. They form deep in the Earth’s crust, experiencing immense temperatures and pressures that can eventually cause partial melting.

Rocks that make up the Lewisian represent several geological events. They formed during the Archean and Paleoproterozoic; that’s between 1.7 and 3 billion years ago!

It includes felsic igneous rocks, e.g. granite, that formed 3 billion years ago, undergoing granulite-facies metamorphism during the Scourian Event around 2.5 billion years ago.

These rocks are crosscut by black basaltic intrusions known as the Scourie Dyke Swarm. They are seen across the Lewisian Complex, forming around 2.4 billion years ago.

Another deformation and metamorphism event occurred 1.7 billion years ago, where partial melting produced a final intrusive event where coarse pink granite sheets cross-cutting all previous rocks.

The Lewisian was eventually exhumed around a billion years ago. At the surface it began to weather and its sediment washed down rivers to form the Torridonian Sandstone.

#geopark #lewisiangneiss #gneiss #metamorphic #laxfordbridge #scotland #scottishhighlands #scottishgeology #walkingscotland #lovescotland #explorescotland #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #geologylife #geologyfieldtrip #amazingscotland #geoscience #earthscience #nc500 #northcoast500 #metamorphicrock #igneous #geologywonders

Aligned alkali feldspar phenocrysts in the Land’s End Granite at Porthcurno.

For scale, the brown, rounded enclave towards the right is approx. 50 mm across.

Alkali feldspar phenocrysts occur in different quantities and sizes across the Cornubian Batholith.

Also called orthoclase or K-feldspar, they’re tabular in shape and possess a crystallographic property known as simple twinning.

A phenocryst is a mineral in an igneous rock that is larger than the groundmass. It’s a textural description and a rock containing phenocrysts can be called a porphyry (adj. porphyritic).

Their larger size could be due to having longer to grow, or if the magma they form in has the right ingredients/conditions to promote growth of that type of mineral.

Alkali feldspar has a low nucleation potential (they don’t like to start growing) but in a magma full of aluminium once they start they grow big!

The Al-rich nature of these granites makes them peraluminous, meaning the total aluminium content outweighs the total sodium + potassium + calcium content.

This gives us an indication of where melts come from that form granite. Sedimentary rocks, particularly clay-rich ones, contain a lot of aluminium. When heated up and metamorphosed they can begin to melt, which is likely to be the source of these granites.

It’s now widely accepted that these phenocrysts form from a crystallising melt. However, reasons for why they occur is still unclear.

It could be they were transported up from a deeper magma chamber. Their size and distribution could be controlled by volatile content in the magma. It could be down to mixing of different intrusions. Or all 3!

The laminar or sometimes more turbulent patterns in their orientation, likely due to magmatic flow during emplacement.

#feldspar #igneous #landsendgranite #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #porthcurno #penwith #geologyfieldtrip #mineralogy #granitecoast #petrology #phenocryst #geologylife #granite #cornishgranite

Stunning large-scale folds in the cliffs just south of Bude.

These flysch sequences are fantastic, and the exposures in the 50 m high cliffs are really impressive. The thickest sandstone beds are around 6-7 metres thick!

They represent major submarine landslides, that could have been triggered by seismic activity at the time.

Flysch is the traditional term for a broadly fining upwards sequence of sandstones and mudstones, deposited from turbidity currents (underwater avalanches) on submarine continental slopes.

These layers of sedimentary rock were originally deposited in the Culm sedimentary basin during rifting around 320 million years ago, in a shallowing ocean basin as more sediment was dumped in it.

Its source isn’t fully resolved, but is probably from a landmass somewhere to the north. It is stratigraphically known as the Bude Formation.

These rocks were buried and folded as Variscan continental collision progressed northwards throughout the Carboniferous.

Cornwall was effectively squeezed together like an accordion in a mountain chain for over 70 million years!

This caused the inversion, or expulsion if you like, of the Culm Basin sedimentary rocks.

This is controlled by the full graben geometry the Culm Basin and pre-existing structures in basement rocks.

#budeformation #flysch #seismic #sedimentary #structuralgeology #tectonic #tectonics #variscan #widemouthbay #cornwall #cornwallcoast #cornishcoast #cornwallgeology #cornishgeology #igcornwall #walkingcornwall #explorecornwall #lovecornwall #lovegeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #geologyfieldtrip #geologylife

Hidden structural treats. Variscan folds in the foreshore at Pendower Beach on the Roseland Peninsula.

I’ve doodled over the 2nd image to make the stand out better. It’s not perfect, but hopefully I get the point across!

These are F1 folds, part of the first phase (D1) deformation these rocks experienced. They have an axial planar cleavage (S1) that becomes bedding parallel away from the fold hinges and is ubiquitous - we see it everywhere across south Cornwall.

Because the fold limbs become parallel away from the fold hinges we would call these isoclinal. Also, the fold axial traces are almost horizontal making them recumbent folds. All this tells us these rocks experienced high levels of strain.

Isoclinal folds can be tricky to spot, given the beds are parallel away from the fold hinge. The lack of clear way up structures in the sedimentary rocks and nebulous fold hinges means they are easily missed.

These rocks part of the Portscatho Formation. They are Upper Devonian, about 375 million years old. They were deformed when caught up between two colliding tectonic plates during the late Devonian and Carboniferous.

This collision, which resulted in the Variscan Orogeny, effectively concertinaed these sedimentary rocks together. Originally horizontal layers of sedimentary rocks buckled and eventually faulted and stacked on top of one another.

Proximal to these folds is probably what was originally a thrust fault, shunting huge volumes of rock toward the NW. However, it is hard to tell as most of these faults were subsequently reactivated by later deformation.

#pendowerbeach #structuralgeology #roselandpeninsula #fault #tectonic #tectonicplates #tectonics #variscan #orogeny #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #geologyfieldtrip #geologylife #amazingcornwall #ukcoast

Complex structural geology at Carne Beach on the Roseland peninsula.

Hidden in this outcrop is evidence of two episodes of regional tectonic deformation. Devonian mudstones and limestones of the Pendower Formation are immediately adjacent to an old tectonic plate boundary, where an ocean closed and two continents collided, an event known as the Variscan Orogeny.

The limestone bed (blue) has been boudinaged as a consequence of high-strain D1 deformation.

Boudinage comes from the French “boudin” which is a type of sausage, because it looks like a string of sausages!

It forms when rock is stretched parallel to primary layering, in this case bedding. Rigid rock, like sandstone or limestone, can break apart along its length when stretched.

The gaps between the broken blocks get infilled by surrounding softer mudstone and precipitated minerals.

It is hard to fathom, but whilst boudinage forms due to extension, here they formed during regional shortening.

In a regime where rocks are sheared there is a direction of maximum extension and a direction of maximum shortening. These axes rotate with increasing strain levels.

Boudinage forms when bedding becomes parallel to the direction of maximum extension, in areas of high strain.

A second deformation phase is also recorded here, occurring during the later stages of Variscan convergence. D2 was lower strain, producing more intermittent, steeply inclined folds.

In this outcrop F2 folds have occurred preferentially about the weaker zone at neck of the boudins.

Looking in detail around the fold hinges you see an axial planar S2 cleavage, which crenulates the earlier S1 cleavage.

An interesting, intricate, and unique outcrop highlighting the complexities of Cornwall’s tectonic history.

#deformation #structuralgeology #pendowerformation #carnebeach #roselandpeninsula #tectonic #tectonics #geologyfieldtrip #variscan #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #geologylife #amazingcornwall #boudinage #limestone

Cornwall Geowalks coming up this November…

St Ives (half-day) - Monday 10th November
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/st-ives-guided-geowalk-half-day-monday-10th-november-2025

Tin Coast (half-day) - Friday 14th November
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/tin-coast-guided-geowalk-half-day-friday-14th-november-2025

Lizard Point (half-day) - Sunday 16th November
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/lizard-point-guided-geowalk-half-day-sunday-16th-november-2025

Praa Sands (half-day) - Sunday 23rd November
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/praa-sands-guided-geowalk-half-day-sunday-23rd-november-2025

Bosigran (half-day) - Friday 28th November
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/bosigran-guided-geowalk-half-day-friday-28th-november-2025

Cornwall Geowalks are guided geology walks around Cornwall’s world-class geological sites and areas of outstanding natural beauty, guided by me! Please see the website for more details. Links in bio.

#geowalks #geotalks #learninggeology #geotours #education #geologyeducation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #cornwallliving #visitcornwall #geologyfieldtrip #geologylife

A ghoulish-looking outcrop for you on Halloween!

This is a very spooky mixed magma intrusions at Kennack Sands on the Lizard peninsula 😱

Kennack Sands, tucked away on the east side of the Lizard, is one of the most fascinating and enigmatic geosites in the UK.

These are intertwined zones of different compositions, including mafic (rich in ferromagnesium minerals), felsic (rich in feldspar + quartz), and composite (mix of felsic + mafic) rocks, adjacent to mantle peridotites of the Lizard Ophiolite.

These rocks formed after Lizard ocean floor spreading had ceased. They appear to occur along thrust faults during ophiolite obduction.

During subduction tectonics oceanic plate gets dragged down below a continental plate due to its higher density. However, fragments can get ripped up by the overriding plate.

Some interpret these rocks as migmatites, forming during high-grade metamorphism that causes partial melting. The felsic rocks from partial melting give rise to the distinct compositional layering.

Others interpret them as magmatic in origin. The mafic magmas intruded first, with the felsic magmas slightly later. These coexisting magmas mingled to form these epic structures. Chemical mixing formed the composite component.

Whilst the spectres of this rocks geological past may be hazy, its pull is strong to geologists at all levels to try and crack the mystery.

If it’s anything like Scooby Doo, then underneath this mask is probably just the janitor!

#gneiss #granite #kennacksands #tectonic #lizard #lizardpeninsula #variscan #ophiolite #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #geologylife #geologyfieldtrip #halloween #scaryrocks

A crenulated cleavage plane catching the light in the Portscatho Formation at Pendower Beach.

Tectonics are continuous but their dynamics can evolve over time. Changes in direction and intensity of stresses in the crust deform rocks differently, which provide a record of how plate tectonics evolve through Earth’s history.

Here we see a cleavage plane that formed during an earlier deformation phase, that has been subsequently deformed (crenulated) and crosscut by a cleavage in a different direction that formed during a later deformation event.

There is a lot we can tell from this. The orientation of the different cleavage planes tells us the direction of maximum shortening during each deformation event so we can understand the regional stress orientation and intensity under which it formed.

The crosscutting relationships also tells us the relative timing of each event, with the cleavage that crenulates the other coming later.

I think this looks like a miniature corrugated iron roof! It is caused by little buckles of the pre-existing cleavage plane that create this amazing pattern.

Because they “kink” a sleek and shiny surface, the light catches differently giving a similar effect to one of those lenticular images that change when you move around it.

Isn’t nature amazing!

#structuralgeology #deformation #tectonic #tectonics #variscan #orogeny #carnebeach #roseland #roselandpeninsula #cornwall #cornwallcoast #cornishcoast #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #cornwalllife #geologylife #platetectonics #walkingcornwall #explorecornwall #lovecornwall #amazingcornwall

Geowalks are back!

After a month off due to the arrival of our baby girl, November and December dates for Geowalks are now available to book!

Lots of exciting adventures await at several epic geolocations around the Cornish coast.

In November there are Geowalks to St Ives, the Tin Coast, Lizard Point, Praa Sands and Bosigran.

In December there are Geowalks to Cape Cornwall, Coverack, St Ives, and the Tin Coast.

Book your place now by visiting www.cornwallgeologist.co.uk/guided-walks. Link in bio.

Can’t find the right date or location for you these months? Well alternatively you can book a personalised, private group walk for you and your family and friends!

Simply contact me by email (sam@cornwallgeologist.co.uk) to find out more.

#geowalks #geotalks #learninggeology #geotours #education #geologyeducation #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #amazingcornwall #cornwallliving #visitcornwall #geologyfieldtrip #geologylife

Last week I visited Hemerdon / Drakelands Mine near Plymouth.

This is my first visit in 10 years, so I was excited to see how the site has changed.

Hemerdon is a tungsten/tin deposit situated in a large granite dyke hosted by Upper Devonian slates on the southwest margin of the Dartmoor Granite.

It is a sheeted vein complex - a series of closely spaced veins composed of mainly quartz, with wolframite and cassiterite. It’s similar to Cligga Head and St Michael’s Mount.

It is associated with a style of hydrothermal alteration called Greisen, resulting in mineral assemblages of quartz+mica±topaz which formed due to the reaction between cooling granite and hot fluids rich in F, B and Li.

Tungsten, designated a critical metal by the UK Government, is essential for things like communication infrastructure, automotive industry, and aerospace sector. It is also has military applications, for strengthening steel and armour-piercing projectiles.

Tungsten West who operate the site are working towards going into production in the second half of 2026.

Hemerdon is the 2nd largest tungsten deposit in the world, and if the mine goes into production it would make the UK the 3rd largest producer.

Along with South Crofty, Hemerdon offers a real opportunity to bring metal mining back to the region. Not only will this be an economic boost, but it will have a positive impact on local society.

Mining is an important part of our culture and heritage, and a return of metal mining will make this last 27 years a blip in its 4,500 year history, rather than an end.

It’s really exciting, and I wish Tungsten West all the best for the future.

A huge thank you to Tungsten West, especially Marica Lyndon, Matt Tonkins, Damian Andrews, and the other staff who showed us around. Thank you also to the RGSC for organising the event.

#tin #tungsten #wolframite #greisen #mineralisation #granite #hemerdon #tungstenwest #devon #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #cornishmining #geologyfieldtrip #geologylife #drakelands #tungstenmine #criticalmetals #ukmining #mininglife #miningindustry #mininguk

Something of geological magnitude has happened to @jennawitts.music and I!

Our beautiful daughter, Eleanor Joy (aka Pebble) was born a couple of weeks ago. Mother and baby did superb after a hectic but fairly rapid labour.

Pebble is a little bundle of perfection, and Jenna and I are settling well into parenthood, albeit fairly stressed!

Thank you for all of your love and best wishes. Apologies if you have messaged in the last few weeks - I will get back to you as soon as I can!

The world has a budding musical geologist!

#babygirl #eleanor #buddinggeologist #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #structuralgeology #geologylife #baby #daughter #littlegirl #babygeologist #newborn #cornishgirl #cornishmaid #cornwalllife

St Ives fossils.

Walking the path above Bamaluz beach I noticed an anomalous building stone in the wall - limestone. This is odd, with very little limestone in Cornwall and definitely none in west Cornwall!

Looking in detail I realised there are loads of limestone blocks. Not only that, but they also contain beautiful fossils!

The limestones are biomicrites (Folk classification scheme), and mudstones-packstones (Dunham scheme). From what I can see there are brachiopods, corals, gastropods, and burrows.

As a structural geo this is the limit of my palaeontology! Apologies for any errors in my assessment and ignorance to get more detail from them!

Thankfully I know the brilliant Kevin Page who is the go-to guy for palaeontology and SW England limestones! He has gratefully shed some light on them and their provenance.

Kevin suggests they are Mid-Devonian in age, and likely either from the Plymouth or Torbay area. They are more Torbay-like than Plymouth, where the limestones are more tectonically ‘stretched’. These are quite well-preserved.

These Devonian limestones formed from carbonate reefs along inter-basinal highs during passive margin rifting. The Plymouth and Brixham limestone formations are two examples of these.

How did they end up in St Ives? This is the site of an old lime kiln, built in the 1830s. It is now the fabulous St Ives Museum. When they built the subsequent wall they must have used what rocks were lying about.

Limestone is used to make quick lime for construction and agriculture. With no limestone occurring naturally it can be imported by barge. Lime kilns are often found along the coast or rivers where imported limestone can be dumped nearby before being roasted.

Nice to see fossils in a place where you wouldn’t expect to find them!

#stives #stivescornwall #paleontology #fossil #limestone #limekiln #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #geologylife #geologyfieldtrip #amazingcornwall #stivesbay #fossils #coral #gastropod

Cornwall’s oldest rocks at the most southerly point of mainland Britain.

The Old Lizard Head Formation , or using its old name the Old Lizard Head Series, is exposed in Polpeor Cove.

In the distance is the Man of War reef, composed of the Man of War Gneiss.

The Old Lizard Head Formation comprises amphibolites facies metasedimentary and metabasic igneous rocks.

The Man of War Gneiss is a coarse-grained, banded, high-grade metamorphic rock. The original rocks (protoliths) before they underwent metamorphism were igneous. However, they range in composition from felsic (tonalite) to mafic (gabbro).

These units occur structurally below the Devonian mantle peridotites that crop out just to the north.

U-Pb zircon age data gives them an age of 500 million years old. It makes these rocks some of the oldest in Southwest England.

The origins of these rocks are uncertain. One theory is that these are basement rocks - old, crystalline rocks on top of which younger rocks form. When a fragment of the Lizard oceanic crust was ripped up and dumped on top of the continent during the Variscan Orogeny it could have included a fragment of basement with it, which is why they are out of position.

Another theory is that they represent a fragment of the upper crust that was thrust on top of SW England from the south during the Variscan Orogeny in the Devonian and Carboniferous. Either way, an important piece of the jigsaw to help us understand our tectonic history!

#oldlizardhead #lizardpoint #metamorphic #tectonic #tectonics #structuralgeology #amphibolite #lizard #lizardpeninsula #variscan #cornwall #cornwallcoast #cornishcoast #walkingcornwall #explorecornwall #lovecornwall #cornwallgeology #cornishgeology #geology #geologyrocks #geolife #geologist #geologistsofinstagram #learninggeology #geoadventure #exploregeology #geologicalwonders #ordnancesurvey #ukcoast #geologyfieldtrip

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sam@cornwallgeologist.co.uk

(+44) 07727 096492

Explore Cornwall's extraordinary geological past with the Cornwall Geologist. Learn all about the dynamic story of Earth's history locked in the Cornish landscape and discover how it has shaped the landscape we see.

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Explore Cornwall's extraordinary geological past with the Cornwall Geologist.
Learn all about the dynamic story of Earth's history locked in the Cornish landscape and discover how it has shaped the landscape we see.