Cornwall Geologist

28/08/2026

Cornwall Geowalks coming up this September…

St Ives (half-day) - Sunday 13th September
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/st-ives-guided-geowalk-half-day-sunday-13th-september-2026

Bosigran and Carn Galver (full-day) - Saturday 19th September
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/bosigran-and-carn-galver-guided-geowalk-full-day-saturday-19th-september-2026

Cape Cornwall (half-day) - Sunday 27th September
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/cape-cornwall-guided-geowalk-half-day-sunday-27th-september-2026

Can’t find the right date or location for this month? Well check to see if there is anything that suits better in October!

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.

27/08/2026

Still spaces available!

Explore the spectacular coastline around Coverack, and discover the geology that lies beneath.

23/08/2026

23/08/2026

I had a guest star at my Cornwall Geology Q+A session down at Geevor Tin Mine Museum last week!

At 10 months old Eleanor is definitely the youngest pebble compared to those I bring along to these sessions! But she is by far the prettiest, obviously stealing the show.

Thank you for those who have come along so far to these Q+A sessions at Geevor. They’ve been so much fun with some awesome questions.

I’ve got my final Q+A session of the summer holidays this Thursday, in the Hard Rock Museum at Geevor Tin Mine. Come on down and say hello!

📸 by Jenna Witts aka mummy.

22/08/2026

Cornwall Geowalks coming up…

Coverack (half-day) - Saturday 29th August
Book now: https://www.cornwallgeologist.co.uk/event-details-registration/coverack-guided-geowalk-half-day-saturday-29th-august-2026

Can't find the right date or location for this month? Well check to see if there is anything that suits better in September!

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.

Explore the spectacular coastline around Coverack, and discover the geology that lies beneath.

21/08/2026

Kennack Gneiss(?).

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

Banded mafic (rich in ferromagnesium minerals), felsic (rich in feldspar + quartz), and composite (mix of felsic + mafic) rocks intertwine with beautiful structures, adjacent to mantle peridotites of the Lizard Ophiolite.

These rocks have sparked debate amongst geologists for centuries. Even their stratigraphic name, the Kennack Gneiss, is controversial.

When did they form? How did they form? Where did they come from?

Not enough space to review in detail, but the general consensus is that 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. This is where the name gneiss is appropriate. 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.

The term gneiss is not appropriate if the rocks are igneous. Mafic rocks would be basalts/gabbros and felsic rocks granite, collectively one could refer to them as composite magma intrusions.

This is still very much up for scientific study. Understanding where these rocks form under the right temperatures and pressures is complex, as is fitting them in the larger tectonic model.

17/08/2026

Bands of granite, aplite and pegmatite at Megiliggar Rocks near Porthleven.

This is actually a boulder that has fallen out of the cliffs.

Megiliggar is famous for spectacular horizontal granite sheets exposed in the cliffs, where magmas from the adjacent Tregonning Granite pluton have injected in to the surrounding slate host rock.

These complex, but beautiful patterns and textures in the sheets formed from the interaction between crystallising magmas and exsolved volatiles (super hot, watery fluids).

Trying to map this transition from magmatic to hydrothermal processes during the final stages of crystallisation continues to be the focus of many geologists.

Its secrets could hold the key to understanding many geological processes, including how hydrothermal ore deposits form and forecasting volcanic eruptions.

Compass for scale.

15/08/2026

Adventure awaits for this budding geologist(?).

Wouldn’t it be cool if these markings in the sand got preserved as some anthropogenic ichnofossils for some geologist of the future to discover in millions of years time!

14/08/2026

Fancy a trip down to the Earth’s mantle?! Well why not book on to the Coverack Geowalk on Saturday 29th August!

Book now: https://www.cornwallgeologist.co.uk/event-details-registration/coverack-guided-geowalk-half-day-saturday-29th-august-2026

Explore the spectacular coastline around Coverack, and discover the geology that lies beneath.

14/08/2026

Usually a lens flare in a photo is annoying. But during an eclipse they are just amazing.