Cobalti-ferriferous Arsenic

I have had the specimen here figured for some time, being one of Mr. Day’s, sent him from Cambourne in Cornwall, about the time that Klaproth published his Chemical and Mineral Observations on the Fossils of Cornwall, dated 1787.

The specimen is more or less covered with a brownish and yellowish Oxide of Iron; the parts which have been long exposed, are of a rather dirty grey colour with very little metallic lustre ; the fresh fracture is a little like broken steel, finely granular, but grey and less brilliant than steel: the streak of the same colour, but rather brighter m lustre when fresh. A forcible blow provokes the arsenical scent, as also heat does. It is fusible by the action of the blow pipe, and gives an intense blue colour to Borax. It is very brittle. Spec. Grav. 5.503 to 7.207.

Analysis by Klaproth of an ore from Dolgooth in Cornwall: