carnotite

{{Infobox mineral | name = Carnotite | category = Vanadate mineral | boxwidth = | boxbgcolor = | image = Carnotit auf fossilisiertem Holz - St-George, Utah.jpg | imagesize = 260px | caption = Carnotite in fossilized wood from St. George, Utah | formula = K2(UO2)2 (VO4)2·3H2O | IMAsymbol=Cnt | strunz = 4.HB.05 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = P21/a | unit cell = a = 10.47 Å, b = 8.41 Å, c = 6.91 Å; β = 103.83°; Z = 2 | color = Bright yellow to lemon-yellow, may be greenish yellow. | 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 = 2 | luster = Dull, earthy; silky when crystalline | refractive = nα=1.750 – 1.780, nβ=1.901 – 2.060, nγ=1.920 – 2.080 | opticalprop = Biaxial (−) | birefringence = δ = 0.200 | pleochroism = | 2V = Measured: 43° to 60°, Calculated: 26° to 36° | streak = yellow | gravity = 4.70 | density = | melt = | fusibility = | diagnostic = | solubility = | diaphaneity = Semitransparent | other = 25px Radioactive, not fluorescent | references = }} thumb|Carnotite from the Happy Jack Mine, Moab, Utah

Carnotite is a potassium uranium vanadate 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. It is a major ore of uranium. It is slightly radioactive.