Carnotite

Carnotite
Carnotite in fossilized wood from St. George, Utah
General
Category	Vanadate mineral
Formula (repeating unit)	K2(UO2)2 (VO4)2·3H2O
Strunz classification	4.HB.05
Crystal system	Monoclinic
Crystal class	Prismatic (2/m) (same H-M symbol)
Space group	P21/a
Unit cell	a = 10.47 Å, b = 8.41 Å, c = 6.91 Å; β = 103.83°; Z = 2
Identification
Color	Bright yellow to lemon-yellow, may be greenish yellow.
Crystal habit	Crusts, earthy masses, foliated and granular aggregates.
Twinning	On {001} as both twin and composition plane
Cleavage	Perfect on {001}, micaceous
Fracture	uneven
Mohs scale hardness	2
Luster	Dull, earthy; silky when crystalline
Streak	yellow
Diaphaneity	Semitransparent
Specific gravity	4.70
Optical properties	Biaxial (-)
Refractive index	nα=1.750 - 1.780, nβ=1.901 - 2.060, nγ=1.920 - 2.080
Birefringence	δ = 0.200
2V angle	Measured: 43° to 60°, Calculated: 26° to 36°
Other characteristics	Radioactive, not fluorescent
References

Carnotite is a potassium uranium vanadate radioactive mineral with chemical formula K₂(UO₂)₂(VO₄)₂·3H₂O. The water content can vary and small amounts of calcium, barium, magnesium, iron, and sodium are often present.

Carnotite is a bright to greenish yellow mineral that occurs typically as crusts and flakes in sandstones. Amounts as low as one percent will color the sandstone a bright yellow. The high uranium content makes carnotite an important uranium ore and also radioactive. It is a secondary vanadium and uranium mineral usually found in sedimentary rocks in arid climates.

In the United States it is an important ore of uranium in the Colorado Plateau region of the United States where it occurs as disseminations in sandstone and concentrations around petrified logs. It also occurs in the U.S. states of Wyoming, Colorado, Arizona and Utah. It also occurs incidentally in Grants, New Mexico and Carbon County, Pennsylvania.