Feldspar

A group of common rock-forming aluminium silicate minerals, crushed and used chiefly as a flux in ceramics and glassmaking.

Historical usage

Feldspar's best-known British mining history is bound up with one factory: when John Caldwell Bloomfield inherited the Castle Caldwell estate at Belleek, County Fermanagh, in 1849, he commissioned a geological survey as an amateur mineralogist, which found feldspar, kaolin, flint, clay and shale on his land. Those deposits, worked commercially at Larkhill around eight miles away, supplied the pottery David McBirney and Robert Williams Armstrong founded at Belleek in 1857, and fed the porcelain body Belleek became famous for from 1863 onward.

How it worked

At Belleek, feldspar and the pottery's other raw minerals were ground into slip — the liquid clay mixture potters use to build ware — by a mill wheel powered by the River Erne at Rose Isle.

Why it was used

Feldspar's alumina and silica content lets it act as a flux, lowering the melting point of the ceramic or glass mixture it's added to and helping bind the fired body into a strong, glassy matrix. At Belleek, a high proportion of feldspar to kaolin in the porcelain body was central to the factory's hard, delicate porcelain and its distinctive iridescent glaze.

Value over time

As a bulk industrial mineral rather than a metal, feldspar's value has always been set by tonnage for its end use rather than by any dramatic price history; the Larkhill deposit's value, specifically, was tied entirely to Belleek Pottery's continuing demand rather than to a wider market.

Hazards & challenges

Ordinary hard-rock quarrying and crushing hazards apply — chiefly exposure to silica dust — with no additional hazard specific to feldspar itself well documented.

Risks & limitations

Britain has few large-scale feldspar deposits, so unlike bulk stone or coal it was never a major British mineral industry outside a small number of localities feeding specific factories, and it has always competed against larger, better-established Continental European sources.

Regional variation

Larkhill, County Fermanagh, is the standout British locality worked specifically to supply Belleek Pottery; feldspar occurs far more widely within Britain's granite districts, including Cornwall, but has rarely been worked there as a commodity in its own right.

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.

• Castlecaldwell Feldspar Mine — County Fermanagh (well documented example)
  Named 11 times in this record, first in the summary: “A feldspar and kaolin working at Larkhill on the Castlecaldwell estate,…”

See every mine that worked feldspar →

Sources

1. (primary) Bulk minerals, mineral resources, Northern Ireland — British Geological Survey (Earthwise)
2. (secondary) Company History — Belleek Pottery

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