AUTUNITE or CALCO-URANITE, a mineral which is one of the "uranium micas," differing from the more commonly occurring torbernite (q.v.) or cupro-uranite in containing cal cium in place of copper. It is a hydrous uranium and calcium phosphate, Though closely re sembling the tetragonal torbernite in form, it crystallizes in the orthorhombic system and is optically biaxial. The crystals have the shape of thin plates with very nearly square outline. An im portant character is the perfect micaceous cleavage parallel to the basal plane, on which plane the lustre is pearly. The colour is sulphur-yellow, and this enables the mineral to be distinguished at a glance from the emerald-green torbernite. Hardness 2-2k; specific gravity 3.o5-3.19. Autunite is usually found with pitchblende and other uranium minerals.