Gerstley borate is also referred to as Calcium borate, it supplies B2O3, CaO, other fluxes, SiO2, and Al2O3. Gerstley borate is a calcium borate ore containing the mineral Ulexite ( 3CaO Na2O 5B2O3 16H2O ), along with accessory minerals such as Bentonite, Colemanite, and Probertite. Gerstley borate was formed in marshes and drying lake basins during the Miocene (10 million years ago).
Gerstley borate is named after James Gerstley, former managing director of Borax Consolidated Ltd. It is manufactured by U.S. Borax and Chemical Corp.; the mine is located near Death Valley, CA.
G.B. is an inexpensive source of B2O3 and CaO in glazes. It is often used in place of colemanite.
(courtesy of glazy.org)
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