Skip to main content
Discover Cornwall’s landscape

The Geology of Cornwall

Granite moors, folded sea cliffs, a slice of ancient ocean floor and some of the richest mineral veins in the world – an introduction to the rocks that shaped Cornwall’s landscape, coastline and history.

Geology guides The Meadfoot Beds Bude & the Culm Coast Bodmin Moor Granite The Lizard Serpentine Penwith Granite & Mines St Austell China Clay

By Martin Frost, Cornwall Online

Last updated 13 October 2026

An introduction to Cornish rocks

Cornwall’s scenery is a direct reflection of what lies beneath it. The high, open moors of Bodmin Moor, Hensbarrow, Carnmenellis and West Penwith are granite. The rolling farmland, wooded valleys and slate cliffs between them are made of much older sedimentary rocks – mudstones, siltstones and sandstones laid down in seas some 400 to 300 million years ago, then squeezed, folded and turned into slate. Cornish miners called these rocks killas.

Two areas stand apart. The Lizard peninsula is built from rocks that formed beneath an ocean, including the green and red serpentine that is carved into ornaments and souvenirs. And on the north coast around Bude, younger Carboniferous rocks have been crumpled into spectacular zig-zag folds that can be seen in the cliffs.

The meeting of granite and killas also made Cornwall rich. Hot fluids from the cooling granite filled cracks with tin, copper and other metals, and altered granite produced the china clay of St Austell – industries that shaped Cornish towns, harbours and people for centuries.

Erosion by rivers, weathering and the sea has since exposed these rocks, creating headlands, coves, cliffs and valleys. In many places the coastline gives an unusually clear view of geological features that are hidden beneath soil and vegetation inland.

Cornwall’s rocks at a glance

  • Oldest: the Lizard Complex, formed around 400 million years ago
  • Most widespread: Devonian slates and sandstones (killas)
  • Youngest bedrock: the granites, about 300–275 million years old
  • Mountain building: the Variscan orogeny, which folded and faulted the region
  • Riches: tin, copper, tungsten and china clay
  • World Heritage: Cornwall and West Devon Mining Landscape (2006)

How Cornwall was made

About 400 million years ago · Devonian

Seas, rivers and an ocean floor

Muds, silts and sands washed into shallow seas and basins on the southern edge of an old continent. In south-east Cornwall these became the Meadfoot Beds and related formations. Further south, new oceanic crust was forming – the rocks that would become the Lizard.

About 360–300 million years ago · Carboniferous

Deep-water sands and muds

Thick layers of sandstone and shale built up in a deep basin across what is now north Cornwall and Devon. These are the Crackington and Bude Formations seen in the cliffs from Boscastle to Bude.

Late Carboniferous · the Variscan orogeny

Continents collide

As the great continents came together to form Pangaea, the region was squeezed from the south. Rock layers were folded, sliced by thrust faults and turned into slate, and the Lizard ophiolite was pushed up onto the land.

About 300–275 million years ago · Early Permian

The granite arrives

Molten rock rose and cooled several kilometres underground to form the Cornubian Batholith. Its high points are now exposed as the granite moors, from Dartmoor in Devon to the Isles of Scilly.

During and after the granite

Metals and clay

Hot mineral-rich fluids deposited tin, copper and other metals in veins (lodes). Later, feldspar in parts of the granite altered to kaolinite, creating the china clay of the St Austell area.

The last 2.6 million years · Ice Ages

Shaping today’s landscape

Cornwall lay beyond the main ice sheets, but freeze–thaw shattered the granite tors and covered slopes in rubbly ‘head’. Changing sea levels left raised beaches and drowned river valleys such as the Fal, Fowey and Tamar.

Back to top ↑

Cornwall’s main rock types

Killas (slates & sandstones)

Devonian and Carboniferous sedimentary rocks, altered to slate during mountain building. They form most of Cornwall’s farmland and much of the coast. Delabole, near Camelford, has quarried Cornish slate for centuries.

Granite

Coarse, crystalline rock made of quartz, feldspar and mica, often with large feldspar crystals. It forms the moors and the dramatic cliffs of Land’s End, and was used for lighthouses, harbours and bridges far beyond Cornwall.

Serpentinite

Altered mantle rock from the Lizard, mottled green, red and black and soft enough to carve and polish. It supports rare plants such as Cornish heath, which grows wild almost nowhere else in Britain.

Greenstones

Old volcanic lavas and intrusions (basalts and dolerites) within the killas, altered to green rocks. Pillow lavas – erupted under the sea – can be seen in places such as Pentire Point near Polzeath.

Elvans

Narrow dykes of fine-grained granite-like rock (quartz porphyry) that cut across the killas. The Cornish word ‘elvan’ is still used by geologists, and many elvans were quarried for building stone.

Hornfels

Killas that was baked by the heat of the granite, making it harder and often spotted. Look for it in a ring around the granite masses – this ‘metamorphic aureole’ is where many mineral lodes are found.

Back to top ↑

Geology across Cornwall

Cornwall is not geologically uniform. Rock types and structures change across the county, so comparing different areas is one of the best ways to understand it.

West Cornwall and Penwith

Granite uplands, mineralised districts and the baked rocks around them explain the landscape around Land’s End, St Just and the Penwith peninsula, where mine engine houses still stand on the cliffs. Read the Penwith guide →

Bodmin Moor

Granite underlies much of the moor. Exposed tors such as Rough Tor and the Cheesewring show how granite weathers along its joints into stacked blocks.

Mid Cornwall and St Austell

The St Austell granite has been altered in places to china clay. The pits and white spoil heaps north of St Austell are one of Cornwall’s most distinctive man-made landscapes. Read the St Austell guide →

North Cornwall

Around Bude, Crackington Haven and Tintagel, strongly deformed sedimentary rocks and high cliffs give classic examples of bedding, folding, faulting and coastal erosion.

South-East Cornwall

Around Looe, Polperro and the Rame peninsula, Devonian rocks – including the Meadfoot Beds – record a complex history. Detailed mapping matters here, as formations may be folded, faulted or overturned.

The Lizard

Britain’s most southerly peninsula is made of rocks that formed beneath an ocean around 400 million years ago – serpentinite, gabbro and related rocks later pushed onto the land.

Back to top ↑

Cornwall geology guides

In-depth guides to individual rock formations and areas of Cornwall. More guides are being added.

South East Cornwall

The Meadfoot Beds

Early Devonian slates, siltstones and sandstones of the Looe Basin – how they formed, how they were folded and faulted, and where to see them at Talland Bay, Polperro, Looe and Whitsand Bay.

Read the guide
North Cornwall

Bude & the Culm Coast

Carboniferous sandstones and shales crumpled into the famous chevron folds of Bude, Millook Haven and Crackington Haven.

Read the guide
The Lizard

The Lizard Serpentine

Britain’s classic ophiolite – serpentinite, gabbro and dykes from an ancient ocean floor, pushed onto the land during the Variscan orogeny.

Read the guide
Bodmin Moor

Bodmin Moor Granite

The granite of Bodmin Moor, its tors such as the Cheesewring and Rough Tor, and the quarrying and mining that grew up around it.

Read the guide
West Cornwall

Penwith Granite & the Mining Coast

The Land’s End granite, the baked rocks around it, and the tin and copper lodes worked at Botallack, Levant and St Just.

Read the guide
Mid Cornwall

St Austell Granite & China Clay

How the St Austell granite turned to china clay, the white tips of Clay Country, Wheal Martyn and the Eden Project pit.

Read the guide
Back to top ↑

Tin, copper and china clay

Cornwall’s mineral wealth comes from the granite. As it cooled, hot fluids rich in tin, copper, tungsten, arsenic, lead and zinc moved through fractures in the granite and the surrounding killas, depositing metal ores in narrow veins called lodes. Most of the main lodes run roughly east–west and can be followed for kilometres.

Tin has been worked in Cornwall since prehistoric times, first from stream gravels and later from deep hard-rock mines. In the 18th and 19th centuries Cornwall was one of the world’s leading producers of copper and tin, and the engine houses that still stand on the cliffs and moors are part of the Cornwall and West Devon Mining Landscape World Heritage Site.

China clay is the other great Cornish mineral industry. In the St Austell granite, feldspar has been altered to soft white kaolinite, which has been dug and washed out since the 18th century for porcelain, paper and many other uses. The Eden Project is built in a former china clay pit. Read more about the geology of china clay →

Mining heritage to explore

Cornish Mining World Heritage Site
Back to top ↑

Where to see Cornwall’s geology

Talland Bay

Steeply tilted Meadfoot slates and sandstones form ridges of rock pools on the foreshore between Looe and Polperro.

Talland Bay village guide →

Polperro & Looe

Folded Devonian strata in the cliffs and harbour walls, with coast path walks linking the two.

Polperro · Looe

Whitsand Bay

Long cliff-backed sands in south-east Cornwall, with Devonian slates exposed on the shore at low tide.

Whitsand Bay beaches →

The Cheesewring, Bodmin Moor

A natural stack of weathered granite slabs above the old quarry at Minions, surrounded by mining remains.

Bodmin Moor geology guide · Minions village guide

Bude & Millook Haven

Classic chevron folds in Carboniferous sandstone and shale, best seen from the beach at low tide.

Bude geology guide · Millook · Crackington Haven · Bude beaches

The Lizard

Serpentine coves such as Kynance Cove, and the gabbro and dykes of Coverack, on Britain’s most southerly peninsula.

Lizard geology guide · Lizard beaches
Check tide times before exploring the foreshore, keep away from the base of cliffs, and please don’t hammer rock exposures – many sites are protected as Sites of Special Scientific Interest.
Back to top ↑

Cornwall geology FAQ

Most of Cornwall is built from Devonian and Carboniferous sedimentary rocks – slates, mudstones, siltstones and sandstones known locally as killas. Rising through them are the granite masses of Bodmin Moor, Hensbarrow (St Austell), Carnmenellis, Land’s End and the Isles of Scilly. In the far south, the Lizard is made of an entirely different suite of rocks: a slice of ancient ocean floor.

The granites belong to the Cornubian Batholith, a single huge body of granite that runs beneath Devon and Cornwall. It was intruded in stages roughly 300 to 275 million years ago, at the end of the Carboniferous and in the Early Permian. Bodmin Moor and Carnmenellis are among the older masses; the Land’s End granite is one of the youngest.

Killas is the old Cornish miners’ word for the slate and other altered sedimentary rock that surrounds the granite. Near the granite contacts the killas was baked by the heat of the intrusions, producing hard, spotted ‘hornfels’. Many of Cornwall’s richest tin and copper lodes run through the killas close to the granite.

The Lizard peninsula is one of the best-preserved ophiolites in Britain – a section of oceanic crust and upper mantle that formed around 400 million years ago and was later pushed (obducted) onto the edge of the continent during the Variscan mountain-building episode. That is why the Lizard has serpentinite, gabbro and basalt dykes rather than the slate and granite found elsewhere in Cornwall.

China clay (kaolin) forms where the feldspar crystals in granite have been altered to the soft white clay mineral kaolinite. The largest deposits are in the St Austell granite, where the clay has been worked since the 18th century; the white spoil tips and pits around St Austell are the result.

As the granite cooled, hot mineral-rich fluids circulated through cracks in the granite and the surrounding killas, depositing tin, copper, tungsten, arsenic, lead and zinc in veins called lodes. Tin has been worked in Cornwall since prehistoric times, and the mining landscapes of Cornwall and West Devon were inscribed as a UNESCO World Heritage Site in 2006.

The zig-zag chevron folds of the Carboniferous rocks at Millook Haven, Crackington Haven and along the cliffs around Bude are among the most photographed in Britain. In south-east Cornwall, steeply tilted Devonian Meadfoot slates and sandstones can be seen on the foreshore at Talland Bay near Polperro.

Picking up a loose pebble on an open beach is generally fine, but please do not hammer cliffs or outcrops. Many of Cornwall’s best geological sites are protected as Sites of Special Scientific Interest, and some are owned by the National Trust. Always check tide times and keep away from the base of cliffs, which can be unstable.

Back to top ↑

Further reading

This page is a general introduction for visitors. Rock types can change over short distances, and coastal exposures may be folded, faulted or overturned, so a photograph alone is not enough to identify a formation – use the British Geological Survey maps and memoirs for detail.
Page views: 27 ·  2026 views: 27