Coconinoite

Coconinoite is a uranium ore that was discovered in Coconino County, Arizona. It is a phosphate mineral; or uranyl phosphate mineral along with other subclass uranium U6+ minerals like blatonite, boltwoodite, metazeunerite and rutherfordine.

Coconinoite
Coconinoite on a sandstone matrix
General
CategoryPhosphate minerals
Formula
(repeating unit)		Fe3+2Al2(UO2)2(PO4)4(SO4)(OH)2•20(H2O)
Strunz classification8.EB.35
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupC2/c
Unit cella = 12.45(6) Å, b = 12.96(3) Å,
c = 17.22(5) Å; β = 105.7°; Z = 4
Identification
Formula mass489.01 gram/mol
ColorPale creamy yellow
Crystal habitAs lathlike to platy grains, in microcrystalline aggregates seams and crusts.
Mohs scale hardness1-2
LusterAdamantine - pearly
StreakWhite
DiaphaneityTranslucent
Specific gravity2.70
Optical propertiesBiaxial (-)
Refractive indexnα = 1.550 nβ = 1.588 nγ = 1.590
Birefringenceδ = 0.040
PleochroismX = colorless; Y = Z = pale yellow. Orientation: Y = elongation of laths with positive elongation; Y at 8°-25° to elongation of laths with negative elongation.
2V angleMeasured: 28° to 43°, Calculated: 24°
Other characteristics Radioactive
References[1][2][3]

Composition

The chemical formula is Fe2Al2(UO2)2(PO4)4(SO4)(OH)2·20H2O.[4] The chemical formula was derived from the spectrographic analysis.[4]

Physical properties

The mineral has a white streak and a pale creamy yellow color. The mineral occurs as microscopic crystals, the largest found is 6 by 20 micrometers. It is a radioactive mineral, but not fluorescent.[4] Upon heating for dehydration it is found that the mineral loses some of its SO2 at 600 to 800 °C.

Geologic occurrence

It occurs in the oxidized zone of vanadium-poor Colorado Plateau-type uranium deposits of Utah and Arizona. It occurs in association with gypsum, jarosite, limonite, quartz, clay minerals and coalized wood at the Jomac mine, Utah.[3]

Coconinite was first described in 1966 for occurrences in the Huskon Mines, Cameron, Cameron District and the Sun Valley Mine, Vermillion Cliffs District, Coconino County, Arizona. It was named for Coconino County.[2]

References
  1. Webmineral data
  2. Mindat.org
  3. Handbook of Mineralogy
  4. Young.E, Weeks, A.D, and Merowitz, R. (1996) Coconinoite a new mineral from Utah and Arizona. The American Mineralogist 51, 651-663
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