An intergrowth of diamond or "coffin" shaped crystals of
Heulandite. The greenish color is unusual.
Brownish
Heulandite from India.
Heulandite from Idaho.
CHEMISTRY (Ca,Na2)Al2Si7O18 .6H2O Hydrous calcium, sodium aluminum silicate
CRYSTALLOGRAPHY Monoclinic
CRYSTAL GROWTH AND HABITS Heulandite grows as prismatic to tabular crystals often with a diamond or "coffin" shape. It is also granular to massive.
COLOR AND OTHER OPTICAL PROPERTIES Colorless, white, gray, yellow, green, reddish and orange to brown; transparent to translucent
HARDNESS 3.5 - 4
SPECIFIC GRAVITY 2.1 - 2.2
LUSTER Vitreous to pearly
STREAK White
BREAKABILITY Heulandite has one very good cleavage direction and a subconchoidal to uneven fracture.
OCCURRENCE Heulandite is a zeolite found in pockets of basalt and in highly weathered mafic extrusive igneous rocks.
ASSOCIATED MINERALS Zeolites, Apophyllite, Calcite, Stilbite