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Mineralpedia Details for Olmsteadite

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Olmsteadite

Olmsteadite

Named after Frank Olmstead and first found at the Hesnard mine and later the Big Chief mine, and White Cap mines. All three are zoned pegmatites near Keystone. Olmsteadite was the first secondary transition-metal phosphate containg niobium indicating a paragenetic relationship between Columbite-Tantalite and a phosphate, probably Triphylite. Occurs as thick prismatic, very lustrous, sub-adamantine, deep red-brown, well-developed crystals to 1mm. (Moore, PB et al AM v.61, (1976). South Dakota School of Mines display specimen contain crystals to about 10mm. Can be confused with deep red Sphalerite or dark smoky Quartz, both of which are found in the same matrix of advanced altered phosphate rock with cores of Siderite and Hydroxylapatite.

Ref. Handbook of Mineralogy, Anthony et al (1995) and MSA at http://www.handbookofmineralogy.org/pdfs/olmsteadite.pdf

Formula
KFe2+2NbO2(PO4)2ยท2H2
Crystal System
Orthorhombic 
Crystal Habit
Prismatic 
Cleavage
Good, Good, None 
Luster
Subadamantine 
Color
brown, reddish brown, black 
Streak
olive green 
Class
Orthorhombic - Pyramidal 
Fracture
Brittle 
Hardness
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Olmsteadite from White Cap mine, Pennington Co., South Dakota, United States

Olmsteadite
            from White Cap mine, Pennington Co., South Dakota, United States

Red bladed to tabular crystals, less than 1cm.

Click thumbnail images for larger view.

Olmsteadite from Big Chief mine, Pennington Co., South Dakota, United States

Olmsteadite
            from Big Chief mine, Pennington Co., South Dakota, United States

Deep red tabular crystals to 1cm in Siderite.

Click thumbnail images for larger view.

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