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MINERALS AND MINING 87 the Delabole quarry is the most renowned, have already been mentioned. At Calstock and Gunnislake a few years ago there were numerous miners engaged in the manufacture of arsenic from the waste product of the abandoned copper But now this has become an extinct industry. mines. Shipping Slate, Port Gavin Wulfram or tungsten, a metal used as an alloy for hardening steel, was also a waste product from the tin mines, but it is now utilised. At St Ives, pitchblende is now being worked for radium.
