Gerstleyite Locality: Baker mine, U.S. Borax Mine (Pacific West Coast Borax; Pacific Coast Borax County; Boron Mine; U.S. Borax and Chemical Corp.; Kramer Mine; Baker Mine), Kramer Borate deposit, Boron , Kramer District, Kern County , California , USA ( Locality at mindat.org ) Size: miniature, 4 x 3 x 2 cm Gerstleyite Gerstleyite is an extremely rare sulfosalt , in fact I'd warrant so rare on the market that most people, even diehard sulfide lovers, have never seen one. This was the first known sodium sulfosalt according to MinDat. This specimen is from the original find and the original collector as reported to me on the label from the previous owner (see below - I trust his sourcing on that information). It is a textbook nodule of crystallized gerstleyite in matrix from this boron open pit mine, collected by a man named Vincent Morgan in 1954. From him, it was sold to a friend who is a very well known collector of rare sulfides and sulfosalts, now a professor of minalogy himself, Frank Keutsch. He told me this is one of a few he obtained long ago. Certainly, this is a good one, and is the best I know of around the market - well, its the ONLY one I know of on the market since I first heard of it a decade ago, put it that way. — Photo: Robert M. Lavinsky · CC BY-SA 3.0
Gerstleyite
Gerstleyite is an IMA-recognized mineral species in the oxides & hydroxide class, with the chemical formula Na₂(Sb,As)₈S₁₃·2H₂O.
It crystallizes in the monoclinic crystal system (space group Cm).
Key properties: Mohs hardness 2.5; specific gravity 3.62; Bright cinnabar-red; powder darkens on exposure streak; Weakly adamantine luster.
IMA symbol Gst, grandfathered status — known before the IMA’s founding, named in 1956.
A low-temperature mineral found embedded in massive borates and clay.
It is found associated with Borax, probertite, tincalconite, realgar, stibnite.
The mineral was named to honor James Mack Gerstley (1907–), President of the Pacific Coast Borax Company.