Coconinoite [Formula: Fe3+2 Al2(UO2)2(PO4)4(SO4)(OH)2•20(H2O)] is a uranium ore that was discovered in Coconino County, Arizona. It is a monoclinic mineral containing aluminum, hydrogen, iron, oxygen, phosphorus, sulfur, and uranium. It is a rare uranium mineral that is named for the type locality from where it was first described, Coconino Co., Arizona, USA. It is an extremely unusual mineral just for its chemistry alone.
Coconinoite is interesting for its good fluorescence under UV light as well. It is a phosphate mineral; or uranyl phosphate mineral along with other subclass uranium U6+ minerals like blatonite, boltwoodite, metazeunerite, and rutherfordine.
- Category: Phosphate minerals
- Formula: Fe3+2 Al2(UO2)2(PO4)4(SO4)(OH)220(H2O)
- Crystal system: Monoclinic
- Crystal class: Prismatic (2/m) (same H-M symbol)
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. Upon heating, for dehydration, it is found that the mineral loses some of its SO2 at 600 to 800°C.
- Formula mass: 489.01 gram/mol
- Color: Pale creamy yellow
- Crystal habit: As lathlike to platy grains, in microcrystalline aggregates seams and crusts.
- Mohs scale hardness: 1-2
- Luster: Adamantine – pearly
- Streak: White
- Diaphaneity: Translucent
- Specific gravity: 2.70
- Optical properties: Biaxial (-)
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.
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.
Remember, this is also a radioactive mineral and should be stored away from other minerals that are affected by radioactivity and human exposure should always be limited.