Powellite

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Powellite
Powellite-288824.jpg
General
CategoryMolybdate minerals
Formula
(repeating unit)
CaMoO4
Strunz classification7.GA.05
Crystal systemTetragonal
Crystal classDipyramidal (4/m)
(same H-M symbol)
Space groupI41/a
Unit cella = 5.222 Å,
c = 11.425 Å; Z = 4
Identification
Formula mass200.02 g/mol
ColorStraw-yellow, greenish yellow, yellow-brown, brown, colorless, may show blue to black zones
Crystal habitFlat tabular crystals often paper-thin on {001}, may be crusty to pulverulent or massive
CleavageIndistinct on {011}, {112} and {001}
FractureConchoidal
Mohs scale hardness3.5-4
LusterAdamantine
Streaklight yellow
DiaphaneityTransparent
Specific gravity4.25
Optical propertiesUniaxial (+)
Refractive indexnω = 1.974 nε = 1.984
Birefringenceδ = 0.010
PleochroismO = blue; E = green
Ultraviolet fluorescenceFluoresces bright yellow under shortwave ultraviolet light, dimmer under longwave
References[1][2][3][4]

Powellite is a calcium molybdate mineral with formula CaMoO4. Powellite crystallizes with tetragonal - dipyramidal crystal structure as transparent adamantine blue, greenish brown, yellow to grey typically anhedral forms. It exhibits distinct cleavage and has a brittle to conchoidal fracture. It has a Mohs hardness of 3.5 to 4 and a specific gravity of 4.25. It forms a solid solution series with scheelite (calcium tungstate, CaWO4). It has refractive index values of nω=1.974 and nε=1.984.[2]

Powellite was first described by William Harlow Melville in 1891 for an occurrence in the Peacock Mine, Adams County, Idaho and named for American explorer and geologist, John Wesley Powell (1834–1902).[2]

It occurs in hydrothermal ore deposits of molybdenum within the near surface oxidized zones. It also appears as a rare mineral phase in pegmatite, tactite and basalt. Minerals found in association with powellite include molybdenite, ferrimolybdite, stilbite, laumontite and apophyllite.[4]

References[edit]

  • Palache, C., H. Berman, and C. Frondel (1951) Dana’s System of Mineralogy, (7th edition), v. II, pp. 1079–1081.

External links[edit]

Media related to Powellite at Wikimedia Commons