James Sowerby in his ‘British Mineralogy’ describes and figures sider the head of ‘Argilla electrica’ or ‘White Tourmaline’ a mineral which was undoubtedly phenacite. The specimen was sent to Sowerb,y by a Mr. Herbert in 1804, and was said to have been found in a mine in St. Just, Cornwall. According to Sowerby's description and from the eoloured plate which he gives of the specimen, the mineral occurred as long-prismatlc, colourless crystals , some of which were doubly terminated and lying upon and partly penetrated by mass of prismatic quartz crystals. The crystals were ‘so divided by cracks and flaws in general as to appear of an opaque whiteness in parts’.