A number of varieties, named on the basis of their hardness and physical appearance, were produced.'Ceramic Raw Materials. W.E.Worrall. The Institute Of Ceramics / Pergamon Press, 1982 Maximum production was achieved in the early 1950s, with around 70,000 tonnes per annum. The largest producer, English China Clays, ceased production in 1973, when Goonvean Ltd became the sole producer. Due to increasing competition from imported alternatives and a contracting domestic market, sales fell from 8,000 tonnes per year to 2,800 tonnes in 2001.'Changes & Developments Of Non-plastic Raw Materials. A. Sugden. International Ceramics, Issue 2 2001.'Mineral Resource Information For Development Plans - Cornwall: Resources And Constraints. British Geological Survey. 1997. Pg. 12 The last quarry closed in 2006.
