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Formula: Fe3+2Al2(UO2)2(PO4)4(SO4)(OH)2.20H2O
Hydrated compound phosphate, uranyl mineral
Crystal System: Monoclinic
Specific gravity: 2.70 measured, 2.68 calculated
Hardness: Soft
Colour: Pale creamy yellow
Common impurities: Fe,Cr
Very strongly RADIOACTIVE
Environments
Coconinoite occurs in the oxidised zone of sandstone-type
uranium deposits in Triassic (252-201 million years ago) strata at four
mines in the Colorado Plateau
(AM 51.651-663).
Localities
At the Harvey Blackwater No. 4 Mine, Yazzie Mesa, Cane Valley Mining District, Apache County, Arizona, USA,
coconinoite was found in the uranium deposit in silty
sandstone
(AM 51.651-663).
There are two co-type localities, Huskon No. 7 mine, Huskon Mines, Cameron, Cameron Mining District, and the Sun
Valley Mine, Marble Canyon, Vermillion Cliffs Mining District, both in Coconino County, Arizona, USA.
At the Huskon No. 7 mine, Huskon Mines, Cameron, Cameron Mining District, Coconino County, Arizona, USA,
coconinoite was identified by its X-ray diffraction powder pattern
(AM 51.651-663).
At the Sun Valley Mine, Marble Canyon, Vermillion Cliffs Mining District, Coconino County, Arizona, USA,
coconinoite was found in seams 1 mm or less thick, predominantly along the bedding planes of a light-coloured,
arkosic sandstone that
is fine grained, poorly sorted, and thinly bedded. Gypsum occurs as visible
crystals with the coconinoite and it is present on joint surfaces
(AM 51.651-663).
At the Jomac Mine, White Canyon Mining District, San Juan County, Utah, USA, coconinoite was first found in a
uranium deposit in sandy
siltstone. It is associated with
gypsum, jarosite,
limonite, quartz,
clay and coalified wood. One sample has crusts of coconinoite on a layer
of gypsum coating buff-coloured
clay.
The association indicates an environment of oxidising pyritic, low-valent
uranium ore. Coconinoite is more likely to occur in
uranium deposits which contain little or no
vanadium or copper
(AM 51.651-663).
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