1911 Encyclopædia Britannica/Torbernite

by Leonard James Spencer

TORBERNITE (or cupro-uranite), a mineral which is one of the “uranium micas”; a hydrous uranium and copper phosphate, Cu(UO₂)₂(PO₄)₂+12H₂O. Crystals are tetragonal and have the form of square plates, which are often very thin. There is a perfect micaceous cleavage parallel to the basal plane, and on this face the lustre is pearly. The bright grass-green colour is a characteristic feature of the mineral. The hardness is 21/2 and the specific gravity 3.5. The radio-activity of the mineral is greater than that of some specimens of pitchblende. It was first observed in 1772 at Johanngeorgenstadt in Saxony, but the best examples are from Gunnislake near Calstock and Redruth in Cornwall. The name torbernite is after Torbern Bergman; chalcolite is a synonym.  (L. J. S.)