Carnotite

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
Carnotite in fossilized wood from St. George, Utah
General
CategoryVanadate mineral
Formula
(repeating unit)		K2(UO2)2
(VO4)2·3H2O
Strunz classification4.HB.05
Crystal systemMonoclinic
Crystal classPrismatic (2/m)
(same H-M symbol)
Space groupP21/a
Unit cella = 10.47 Å, b = 8.41 Å, c = 6.91 Å; β = 103.83°; Z = 2
Identification
ColorBright yellow to lemon-yellow, may be greenish yellow.
Crystal habitCrusts, earthy masses, foliated and granular aggregates.
TwinningOn {001} as both twin and composition plane
CleavagePerfect on {001}, micaceous
Fractureuneven
Mohs scale hardness2
LusterDull, earthy; silky when crystalline
Streakyellow
DiaphaneitySemitransparent
Specific gravity4.70
Optical propertiesBiaxial (-)
Refractive indexnα=1.750 - 1.780, nβ=1.901 - 2.060, nγ=1.920 - 2.080
Birefringenceδ = 0.200
2V angleMeasured: 43° to 60°, Calculated: 26° to 36°
Other characteristics Radioactive, not fluorescent
References[1][2][3][4][5]

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. 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[2] and concentrations around petrified logs. It also occurs in the U.S. states of Wyoming, Colorado, South Dakota, Nevada, Arizona, and Utah. It also occurs incidentally in Grants, New Mexico, and Carbon County, Pennsylvania.[6]

Carnotite is reported in Congo (Kinshasa), Morocco, Australia (Radium Hill) and Kazakhstan.[6] 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.[7] It is named for Marie Adolphe Carnot (1839–1920), French mining engineer and chemist.[4]

Uses

Carnotite is an ore of uranium. At times in the early 20th century, it was mined primarily for radium or vanadium.

The mineral was used to produce quack devices involving radioactive substances.

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. Mineralienatlas
  2. Handbook of Mineralogy
  3. Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York ISBN 0-471-80580-7
  4. Mindat.org
  5. Webmineral
  6. Mindat with locations
  7. 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.
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