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 04.HB.05
Crystal symmetry Monoclinic 2/m
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.
Crystal system Monoclinic; 2/m
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 [1][2][3][4]

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.

Occurrence

Carnotite from the Happy Jack Mine, Utah

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[1] 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.[5]

Carnotite is reported in Congo (Kinshasa), Morocco, Australia (Radium Hill) and Kazakhstan.[5] In Pakistan carnotite occurs in the Upper Miocene middle Siwaliks sandstone (Dhokpathan Formation), in the vicinity of Takhat Nasrati, Karak District.

Name and discovery

The mineral was first described in 1899 by French scientists M. M. C. Freidel and E. Cumenge, who identified it in specimens from Roc Creek in Montrose County, Colorado, United States.[6] It is named for Marie Adolphe Carnot (1839 - 1920), French mining engineer and chemist.[3]

Related mineral species

Several related mineral species exist, including: margaritasite ((Cs,K,H3O)2(UO2)(VO4)2·H2O) and tyuyamunite, (Ca(UO2)2(VO4)2·5-8H2O).

See also

References

  1. 1 2 Handbook of Mineralogy
  2. ↑ Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York ISBN 0-471-80580-7
  3. 1 2 Mindat.org
  4. ↑ Webmineral
  5. 1 2 Mindat with locations
  6. ↑ Robert J. Wright and Donald L. Everhart (1960) Uranium, in Mineral Resources of Colorado First Sequel, State of Colorado Mineral Resources Board, p.330-331.

External links

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