Mineral Species: Colemanite

Chemical Formula: Ca2B6O11.5H2O

Chemical Name: Hydrous Calcium Borate

Mineral Class: Borate

Mineral Notes: Colemanite is ususally found with Borax in large lake deposits in dry regions, for example the California Playa lakes. These form only in rainy seasons due to runoff from nearby mountains. The runoff is rich in boron and is highly concentrated by evaporation in the arid climate. Eventually the concentration is so great that crystals of borax and other boron minerals form. Colemanite is ususally white and characterised by its brilliant luster. The basic structure of contains endless chains of interlocking BO2(OH) triangles and BO3(OH) tetrahedrons with the calciums, water molecules and extra hydroxides interspersed between the chains.

Description: A very nice crystal group of Colemanite on matrix. The faces are super-glassy and have pale amber colour. Some of the faces have showy, very pronounced stepped growth zones. Others show twinning. Overall, an excellent display specimen.

Location: Boron, Kramer District, Kern Co., California, USA.