A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 6000 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.
The sulfate minerals all have one or more sulfate anions (SO4 -2).
Hexahydrite is a hydrous magnesium sulfate mineral, MgSO4ยท6H2O. It has a nonmetallic luster, is usually clearish to whitish, has a white streak, and is fairly soft. It usually occurs as earthy, powdery efflorescence on some rock surfaces.
The sample seen here is hexahydrite powder formed as water leached out material from sedimentary rocks of the Eocene-aged Green River Formation. Identification of this powder as hexahydrite has been confirmed by x-ray diffraction (XRD) analysis.
Locality: lower part of cliffs on the northern side of Interstate 80 in the town of Green River, Sweetwater County, southwestern Wyoming, USA
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Photo gallery of hexahydrite:
www.mindat.org/gallery.php?min= 1891
