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For the political philosophy of Enoch Powell, see Powellism.
Yellow-honey powellite crystal with colorless needles of scolecite, from Yeola, Nasik, Maharashtra, India
(size: 108 x 75 mm, 272 g)
Category Molybdate minerals
(repeating unit)
Strunz classification 7.GA.05
Crystal system Tetragonal
Crystal class Dipyramidal (4/m)
(same H-M symbol)
Space group I41/a
Unit cell a = 5.222 Å,
c = 11.425 Å; Z = 4
Formula mass 200.02 g/mol
Color Straw-yellow, greenish yellow, yellow-brown, brown, colorless, may show blue to black zones
Crystal habit Flat tabular crystals often paper-thin on {001}, may be crusty to pulverulent or massive
Cleavage Indistinct on {011}, {112} and {001}
Fracture Conchoidal
Mohs scale hardness 3.5-4
Luster Adamantine
Streak light yellow
Diaphaneity Transparent
Specific gravity 4.25
Optical properties Uniaxial (+)
Refractive index nω = 1.974 nε = 1.984
Birefringence δ = 0.010
Pleochroism O = blue; E = green
Ultraviolet fluorescence Fluoresces 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 is 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]


  1. ^ Mineralienatlas
  2. ^ a b c Powellite mineral information on Mindat.org
  3. ^ Powellite mineral data on Webmineral
  4. ^ a b Mineral Data Publishing PDF
  • 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