X-ray crystallography of aurichalcite and hydrozincite

X-ray diffraction studies with Weissenberg, precession, and powder cameras show that aurichalcite is orthorhombic B22 1 2 (not Pmma as previously reported) with a=27.2+ or -0.1, b=6.41+ or -0.02, c=5.29+ or -0.03A; observed powder data indexed from these values are given. The morphology of crystals from Mapimi, Mexico, is described; a reported perfect (100) cleavage could not be verified. Measured specific gravity is 3.96+ or -0.03. For hydrozincite from Goodsprings, Nev., known space group and unit cell dimensions were confirmed; twinning about (100) was observed and is illustrated. Indexed powder diffraction data are given. The observed specific gravity is 4.00+ or -0.03.