Killas

The Cornish mining word for the dark, slaty metamorphic rock that makes up most of the country rock of Cornwall and western Devon — not itself an ore, but the rock the tin and copper lodes actually run through.

Historical usage

First recorded in print in 1674 as 'kellus', killas has been in continuous use among Cornish and Devon miners and geologists ever since as the everyday name for the county's dominant slate-like bedrock, distinguishing it from the granite that intrudes through it in places like Bodmin Moor, Dartmoor and the Land's End peninsula.

Why it was used

Miners needed a quick, practical word for the rock they were actually driving through day to day, long before formal geological terminology existed to describe it — killas served that purpose, and stuck, even though it never became a standard term in academic stratigraphy outside Cornwall and Devon.

Regional variation

Confined almost entirely to Cornwall and adjoining west Devon, including the fringes of Dartmoor — a genuinely local word for a genuinely local rock, rather than a term with any currency elsewhere in Britain.

Images

Mines associated with this term

Included only where MineArchive's own research gives a reasonable evidential basis — not every mine where this might plausibly apply.

• Wheal Prosper — Cornwall (well documented example)
  The mine's own recorded workings explicitly describe the surviving engine house as built of killas rubble.

Sources

1. (secondary) Cornish Killas — National Character Area Profiles
2. (secondary) Killas — Wikipedia

Record created: 22 August 2026 · Last researched: 22 August 2026