Brochantite, a mineral species consisting of a basic copper sulphate Cu(OH)SO, crystallizing in the orthorhombic system. The crystals are usually small and are prismatic or acicular in habit; they have a perfect cleavage parallel to the face lettered a in the adjoining figure. They are transparent to translucent, with a vitreous lustre, and are of an emerald-green to blackish-green colour. Specific gravity 3.907; hardness 3½-4. The mineral was first found associated with malachite and native copper in the copper mines of the Urals, and was named by A. Lévy in 1824 after A.J.M. Brochant de Villiers. Several varieties, differing somewhat in crystalline form, have been distinguished, some of them having originally been described as distinct species, but afterwards proved to be essentially identical with brochantite; these are königine from the Urals, brongniartine from Mexico, krisuvigite from Iceland, and warringtonite from Cornwall. Of other localities, mention may be made of Roughten Gill, Caldbeck Fells, Cumberland, where small brilliant crystals are associated with malachite and chrysocolla in a quartzose rock; Rézbánya in the Bihar Mountains, Hungary; Atacama in Chile, with atacamite, which closely resembles brochantite in general appearance; the Tintic district in Utah. A microscopical examination of the green copper ores of secondary origin in the Clifton and Morenci district of Arizona proves brochantite to be of extremely common occurrence mostly intergrown with malachite which effectually masks its presence: it is not unlikely that the malachite of other localities will on examination be found to be intergrown with brochantite.

Mention may be here made of another orthorhombic basic copper sulphate not unlike brochantite in general characters, but differing from it in containing water of crystallization and in its fine blue colour; this is the Cornish mineral langite, which has the composition CuSO·3Cu(OH)+HO.

(L. J. S.)