carnotite

A yellow ore of uranium and radium with composition K(UO₂)₂(VO₄)₂·3H₂O.

[French, after Marie Adolphe Carnot (died 1920), French mining engineer.]

A mineral that is a hydrous vanadate of potassium and uranium, K₂(UO₂)₂(VO₄)₂ · nH₂O. The water content varies at ordinary temperatures from one to three molecules. Carnotite generally occurs as a powder or as a slightly coherent microcrystalline aggregate. Color ranges from bright yellow to lemon- and greenish-yellow.

In the United States the principal region of carnotite mineralization is the Colorado Plateau and adjoining districts of Utah, New Mexico, and Arizona. Carnotite is found also in Wyoming and in Carbon County, Pennsylvania. Deposits are located at Radium Hill near Olary, Australia, and in Katanga (Zaire). Carnotite is the chief source of uranium in the United States. It is also a source of radium and vanadium. See also Radioactive minerals; Uranium; Vanadium.

Environment

Yellow concentrations, coatings, and disseminations in sandstone and limestone sediments. May replace fossil wood, etc. in such sedimentary beds.

Few recognizable crystals; microscopic plates sometimes visible. Usually forms powdery disseminations or films.

Bright yellow. Luster earthy; hardness indeterminate (soft); specific gravity 4.1; crystal plates said to have a basal cleavage , but would not be visible. Powdery and crumbling; opaque like an ocher; not fluorescent.

Hydrous potassium uranium vanadate (10.4% K ₂ O, 63.4% UO ₃ , 20.2% V ₂ O ₅ , 6.0% H ₂ O).

Infusible. Powder turns red-brown when dropped in boiling nitric acid, and dissolves for green solution. Cold borax bead is fluorescent green. Residue of evaporation of acid is fluorescent.

The bright yellow uranium color without the normal uranium fluorescence is significant. A bead test with ultraviolet light will prove uranium.

The only important deposits are in sandstones in w. Colorado and e. Utah, with some in Arizona and New Mexico. Its exact origin is uncertain; presumably it has formed from the alteration of pre-existing uranium and vanadium minerals. It is disseminated through a red-brown sandstone, often replacing fossil wood, then making rich masses of relatively pure carnotite. Yellow stains of carnotite have been found in a conglomerate along a railroad cut at Mauch Chunk, Pennsylvania. It has been found in n. Mexico, at Radium Hill, South Australia, and with the uranium ores at Shaba (Katanga), Zaire. The only actual U.S. crystals seem to be those of small limestone pockets at Grants, New Mexico.

For some years, before the discovery of the Zaire uranium ores, the U.S. carnotite deposits were the world's chief source of radium. The Curies obtained their experimental material from Colorado. These deposits were closed when the development of richer African ores reduced the price of radium. When radioactive interest shifted to uranium they became an important U.S. source of that metal.

Carnotite
General
Category	Mineral
Chemical formula	K2(UO2)2(VO4)2·3H2O
Identification
Color	Yellow, Golden yellow, Greenish yellow
Crystal habit	crusts, earthy masses, foliated and granular aggregates.
Crystal system	Monoclinic; 2/m
Cleavage	perfect: one direction
Fracture	uneven
Mohs Scale hardness	2
Luster	pearly to dull or earthy
Streak	yellow
Specific gravity	4 - 5
Refractive index	nα=1.750 - 1.780, nβ=1.901 - 2.060, nγ=1.920 - 2.080
Other characteristics	Radioactive, not fluorescent

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.

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. 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. Occurs in the states of Wyoming; Colorado; Arizona; Utah; It also occurs incidentally in Grants, New Mexico and Carbon County, Pennsylvania. It is also reported in Zaire; Morocco; Radium Hill, Australia; and Kazakhstan.

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.^[1] It is named for Marie Adolphe Carnot (1839 - 1920), French mining engineer and chemist.

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

• List of minerals
• List of minerals named after people

References

1. ^ 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.

• Hurlbut, Cornelius S.; Klein, Cornelis, 1985, Manual of Mineralogy, 20th ed., John Wiley and Sons, New York ISBN 0-471-80580-7
• Webmineral
• Univ. of Virginia
• Mineral Galleries
• Mindat.org

Carnotite, Happy Jack Mine, Utah

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