Colemanite: Gemstones Information
Colemanite is monoclinic hydrous calcium borate, Ca2B6O115H2O and is commonly colourless to milky white. The hardness is 4.5, the SG 2.42. The RI is 1.586, 1.592 and 1.614, biaxial positive.Colemanite usually fluoresces whitish or green under UV. Equant to short-prismatic crystals are brittle and fashioning of transparent specimens is difficult. California produces most facetable specimens, especially from the Death Valley and Boron areas.Colemanite is a common constituent of borate deposits formed in sodium- and carbonate-poor lake environments.