Halide minerals

name colour lustre Mohs hardness specific gravity

atacamite various bright green shades; dark emerald-green to blackish adamantine 3–3½ 3.8

calomel colourless, white, grayish, yellowish, brown adamantine 1½ 7.15

carnallite milk-white; sometimes reddish (from included hematite) greasy, dull to shining 2½ 1.6

cerargyrite colourless when pure and fresh; usually gray; becomes purple or violet-brown on exposure to light (cerargyrite) hornlike 2½ 5.6 (AgCl) to 6.5 (AgBr)

cryolite colourless to white, brownish, reddish, brick red vitreous to greasy 2½ 3.0

fluorite variable vitreous 4 3.2

halite colourless when pure, often splotched blue or purple vitreous 2 2.2

sal ammoniac colourless, white, grayish, yellow vitreous 1–2 1.5

sylvite colourless, white, grayish, bluish, or red (from included hematite) vitreous 2 2.0

name habit or form fracture or cleavage refractive indices crystal system

atacamite brittle, transparent to translucent tabular to slender prismatic crystals one perfect cleavage alpha = 1.831

beta = 1.861

gamma = 1.880 orthorhombic

calomel tabular crystals; drusy crusts; earthy masses one good cleavage omega = 1.956–1.991

epsilon = 2.601–2.713 tetragonal

carnallite granular, massive conchoidal fracture alpha = 1.465–1.466

beta = 1.474–1.455

gamma = 1.444–1.446 orthorhombic

cerargyrite crusts; waxy coatings; hornlike masses uneven to subconchoidal fracture n = 2.071–2.253 isometric

cryolite coarsely granular masses no cleavage alpha = 1.338

beta = 1.338

gamma = 1.339 monoclinic

fluorite brittle, transparent or translucent cubes and two-cube penetration twins perfect octahedral cleavage n = 1.432–1.437 isometric

halite transparent cubic (often cavernous or stepped) crystals; granular masses perfect cubic cleavage n = 1.544 isometric

sal ammoniac skeletal aggregates conchoidal fracture n = 1.639 isometric

sylvite transparent cubes or granular masses perfect cubic cleavage n = 1.490 isometric