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Title: Coconinoite  
Author: World Heritage Encyclopedia
Language: English
Subject: Phosphate minerals
Collection: Aluminium Minerals, Iron Minerals, Monoclinic Minerals, Phosphate Minerals, Uranium Minerals
Publisher: World Heritage Encyclopedia


Category Phosphate minerals
(repeating unit)
Strunz classification 08.EB.35
Crystal symmetry Monoclinic 2/m
Unit cell a = 12.45(6) Å, b = 12.96(3) Å, c = 17.22(5) Å; β = 105.7°; Z=4
Formula mass 489.01 gram/mole
Color Pale creamy yellow
Crystal habit As lathlike to platy grains, in microcrystalline aggregates seams and crusts.
Crystal system Monoclinic
Mohs scale hardness 1-2
Luster Adamantine - pearly
Streak White
Diaphaneity Translucent
Specific gravity 2.70
Optical properties Biaxial (-)
Refractive index nα = 1.550 nβ = 1.588 nγ = 1.590
Birefringence δ = 0.040
Pleochroism X = 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 angle Measured: 28° to 43°, Calculated: 24°
Other characteristics Radioactive
References [1][2][3]

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


  • Composition 1
  • Physical properties 2
  • Geologic occurrence 3
  • References 4


The chemical formula is Fe2Al2(UO2)2(PO4)4(SO4)4(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 micrometres. It is a radioactive mineral, but not fluorescent.[4] Upon heating for dehydration it is found the that mineral losses 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]


  1. ^ Webmineral data
  2. ^ a b
  3. ^ a b Handbook of Mineralogy
  4. ^ a b c 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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