Carnotite

Information about Carnotite

Carnotite is a secondary potassium uranium vanadate mineral – one of the principal uranium ore minerals of the Colorado Plateau – forming bright canary-yellow to lemon-yellow powdery to earthy masses and occasionally tiny platy crystals in the sandstone uranium deposits of the western United States.

It is not a showy mineral for collectors in the way that autunite or torbenite are, but it is scientifically important as a major source of uranium and vanadium, and has one of the more eventful histories of any ore mineral in the twentieth century.

It typically occurs as powdery, earthy, or microcrystalline yellow masses disseminated through sandstone, concentrated around carbonised wood fragments and organic material, or in thin seams and coatings. Individual crystals are monoclinic, tabular to platy, but are rarely large enough to be visible to the naked eye.

The colour – a vivid, almost fluorescent canary to lemon yellow – is one of the most distinctive in mineralogy, shared by only a few other uranium and vanadium minerals, and is reliable as a field indicator in the right geological context.

Carnotite is radioactive. It forms as a secondary mineral by the oxidation and redistribution of primary uranium minerals in roll-front and tabular sandstone uranium deposits, where uranium-bearing groundwater encounters organic material or other reducing agents that precipitate the uranium as secondary minerals.

Uses and History

Carnotite was historically the principal ore from which uranium and radium were extracted during the early twentieth century. The discovery of radioactivity by Henri Becquerel in 1896 and the subsequent isolation of radium by Marie and Pierre Curie in 1898 – from pitchblende, not carnotite – created enormous demand for uranium minerals across the world.

Carnotite from the Paradox Basin deposits of Colorado and Utah became a primary source of radium during the early twentieth century, and the Curies themselves used carnotite from Colorado in their later radium extraction work.

During the Second World War and the subsequent Cold War nuclear weapons programmes, the Colorado Plateau carnotite deposits became central to American uranium supply, and the region was intensively mined through the 1940s-1970s. The vanadium content of carnotite deposits was also separately valuable – vanadium is used as a steel-strengthening alloy – and vanadium was extracted alongside uranium from the Colorado Plateau ores.

The mineral was first described in 1899 by the French chemists Friedel and Cumenge, from specimens collected in the Montrose County area of Colorado. It was named in honour of Marie Adolphe Carnot (1839-1920), a French mining engineer, chemist, and Inspector-General of Mines who had studied uranium minerals and contributed to analytical chemistry.

Mineralogy

Hazards and Warnings

Radioactive mineral. Handle with care.

Specimens should be stored in sealed containers, handled with care, and kept well away from prolonged close contact with the body. Do not inhale dust. Wash hands thoroughly after handling. Children should not handle carnotite specimens.

A Geiger counter is strongly recommended for any uranium mineral collection. Please see our information on handling radioactive minerals for full guidance.

Almost all rocks, minerals (and, frankly, almost all other substances on earth) can produce toxic dust when cutting, which can cause serious respiratory conditions including silicosis. When cutting or polishing rocks, minerals, shells, etc, all work should be done wet to minimise the dust, and a suitable respirator or extraction system should be used.

Translations

Further Reading / External Links

• https://en.wikipedia.org/wiki/Carnotite
• https://www.mindat.org/min-898.html
• https://www.handbookofmineralogy.org/pdfs/carnotite.pdf