Elvan

The Cornish and Devon miners' name for the quartz-feldspar-porphyry dykes that cut across the region's tin and copper lodes — from the Cornish elven, 'spark'.

Historical usage

Elvan dykes were intruded into the Mylor Slates and surrounding country rock around 280-285 million years ago, a later phase of the same granite-related igneous activity that produced Cornwall's tin and copper mineralisation. Miners recognised early on that the dykes' distribution broadly tracked that of the hydrothermal tin-bearing veins they were following underground, making elvan a useful, if imperfect, guide when prospecting.

How it worked

At some mines an elvan dyke appears to have directly controlled where a lode was deposited — at Wheal Coates, for instance, a tin lode developed along the footwall of an elvan dyke — while at others a broad, highly mineralised elvan itself crossed several separate lodes. Later mineral-bearing fluids from the same cooling granite deposited the tin and copper ores in fissures cutting through and around the elvan, chiefly trending east-north-east.

Why it was used

Beyond its role as a guide to ore, elvan's hardness and fine grain made it a valued building stone in its own right — quarried varieties such as Pentewan, Polyphant and Catacleuse stone were prized for finely carved work like doorways — and it was later quarried in bulk for road-building aggregate.

Risks & limitations

Most elvan quarries are now disused, their stone displaced first by other building materials and later by imported aggregate; its usefulness as an ore-prospecting guide was also always partial, since not every elvan dyke controlled or accompanied worthwhile mineralisation.

Regional variation

A term specific to Cornwall and Devon, where these dykes are common; the same kind of quartz-porphyry intrusion occurs elsewhere in Britain but is not locally called elvan outside the south-west.

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.

• Cann Quarry — Devon (well documented example)
  Named 5 times in this record, first in the history: “…jointly from 1874. By 1839 the quarry was also raising porphyritic elvan stone alongside slate, and by the time Edward Gullett took the lease…”
• Hingston Down Quarry — Cornwall (well documented example)
  Named 3 times in this record, first in the summary: “A granite (elvan) quarry above Gunnislake that has worked continuously since 1924,…”

Sources

1. (secondary) Elvan — Wikipedia
2. (secondary) Granite porphyry (Elvan) - St Austell — Virtual Microscope (Open University)

Record created: 27 August 2026 · Last researched: 27 August 2026