Gerstleyite

General Information:
 Chemical Formula:
Na2(Sb,As)8S13·2(H2O)
 Composition:
(Molecular Weight = 1,426.04 gm)
Sodium 3.22 % Na
Antimony 59.76 % Sb
Arsenic 5.25 % As
Hydrogen 0.28 % H 
Sulfur 29.23 % S 
Oxygen 2.24 % O 
 Empirical Formula:
Na2Sb7AsS13·2(H2O)
 Environment:
Sedimentary borate deposits.
 Locality:
Baker Mine, Boron, Kern Co. California.
 Name Origin:
Named for J. M. Gerstley (1907-), President, Pacific Coast Borax Company.
Physical Properties:
 Cleavage:
[010] Perfect, [100] Perfect, [001] Indistinct
 Color:
vermilion or black.
 Density:
3.62
 Habits:
Platy - Sheet forms (e.g. micas)., Fibrous - Crystals made up of fibers., Spherical - Spherical, rounded aggregates.
 Hardness:
2.5 - Finger Nail
 Luster:
Adamantine
 Streak:
vermilion
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