Cupreous Arseniate of Iron

This substance, which is rare in Cornwall, we understand has been brought from Siberia by Professor Pallas, according to Mr. Chenevix, to whom we are obliged for the analysis of it, and to Count Bournon for the most accurate account of its crystallization, which agrees with our specimens. It is found in the Muttrel mine along with cubic Arseniate of Iron. The crystals are always small, generally clustered, more or less in bundles or confused. The individuals form rhomboidal prisms having the two opposite angles very obtuse; and consequently the two others are very acute, terminating with four scalene triangular faces, fixed lower on the acute angles than on the obtuse ones. We cannot be certain that the angle bearing upon the obtuse side of the pyramid is not a right angle: see the geometrical figure. The upper specimen is a largish collection of clusters variously grouped, the clusters formed of crystals diverging from a centre, with the faces of the pyramid only exposed. it is on an irregular gangue of white Quartz with some blackish lumps of gray Sulphuret of Copper, and a few rectangular plates, perhaps Uranite. The left hand bottom figure represents a specimen with more distinct crystals looking like spiculæ, scattered in the hollows of an ochraceous gangue. These sometimes expose one, and the others both ends: see the lower figure. These crystals are mostly of a light shining sage green.