Mundic

The Cornish and Devon word for iron pyrite (and, by extension, related sulphide minerals such as arsenopyrite) found alongside tin and copper ore in a mine's lodes — worthless, and often actively troublesome, waste rock rather than the metal being sought.

Historical usage

Mundic occurs abundantly in the tin and copper lodes of Cornwall and Devon, and generations of miners raised and dumped vast quantities of it as waste alongside their genuine ore. The word survives today mainly through the 'mundic block problem': between around 1900 and 1965, mine waste containing mundic was widely used as aggregate in concrete blocks across Cornwall and west Devon, and the slow oxidisation of the pyrite within those blocks — reacting with water and oxygen to form sulphate, which expands and destroys the concrete's structural integrity — has caused serious, ongoing problems for buildings constructed from them, still a live concern for surveyors and mortgage lenders in the region today.

Why it was used

Miners needed a quick, everyday word to distinguish the pyrite-bearing waste rock that came up alongside genuine tin or copper ore from the valuable mineral itself — mundic served that purpose on the dressing floor as much as underground, wherever ore had to be sorted from worthless sulphide-rich rock.

Risks & limitations

Mundic-rich rock could complicate ore processing, since arsenopyrite in particular had to be roasted off before the underlying tin or copper could be smelted cleanly; its long afterlife as a building-aggregate hazard, discovered only decades after mining had ended, shows how a mine's waste rock could keep causing problems long after the mine itself was forgotten.

Regional variation

A specifically Cornish and Devon term, tied to the tin and copper lodes of the South West rather than being general British mining vocabulary.

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.

• New Consols Mine — Cornwall (well documented example)
  The mine's own recorded history explicitly describes extensive arsenic-processing plant added to roast mundic-rich ore.

Sources

1. (secondary) Mundic — Wikipedia
2. (secondary) Mundic Info — Petrolab

Record created: 23 August 2026 · Last researched: 23 August 2026