# Autunite - Page: https://taslar.bumba.tr/en/stones/autunite/ - Turkish: Otunit - Kind: Mineral - Classification: Minerals › Phosphates - Chemical formula: Ca(UO₂)₂(PO₄)₂·10–12H₂O - Crystal system: Tetragonal - Hardness (Mohs): 2–2.5 - Specific gravity: 3.05–3.2 g/cm³ - Lustre: Vitreous (glassy), Pearly - Transparency: Transparent, Translucent - Colours: lemon yellow, sulfur yellow, greenish yellow, pale green, dark green - Streak: Pale yellow - Cleavage: Perfect on {001}; indistinct on {100} - Fracture: Splits into thin plates along its perfect cleavage - Value ladder: 3/9 step, Building and industrial stone - Last checked: 2026-10-04 The uranium mineral that glows green-yellow under ultraviolet light: beautiful but radioactive. Autunite is a mineral made of calcium, uranium, phosphate and water (Ca(UO₂)₂(PO₄)₂·10–12H₂O). It crystallises as thin square plates in colours from lemon yellow to greenish yellow. Under ultraviolet (UV) light it glows a strong green-yellow. Because it contains uranium it is radioactive, and it is also used as a uranium ore. It was found near the town of Autun in France in 1852 and named after it. ## How does it form? Autunite is a **secondary mineral**: it forms when primary uranium minerals such as uraninite break down on contact with air and water (under oxidising conditions). It is therefore found near the surface of hydrothermal veins, granite pegmatites and similar settings. It occurs with other secondary uranium minerals such as meta-autunite, torbernite, uranophane and sabugalite. Its crystals can grow up to 2 cm. According to the Handbook of Mineralogy, autunite is widespread, but few places yield outstanding specimens. Known localities include the Autun district and the Gagnol mine in Puy-de-Dôme in France (large crystals), Sabugal and Urgeiriça in Portugal, Bergen in the Vogtland, Germany (large crystals), Cornwall in England, and the Daybreak mine in Washington State, USA (fine groups). ## What is it used for? - **Uranium ore:** Because of its high uranium content it is used as a uranium ore. - **Fluorescence displays:** Because it glows strongly under ultraviolet light, it is a well-known specimen in collections of fluorescent minerals. - **Science:** It shows how uranium moves and is deposited near the Earth's surface. ## How to recognise it - Lemon yellow, sulfur yellow or greenish yellow, as thin square or octagonal plates; often forms scaly crusts. - Glows a strong green-yellow under ultraviolet light (fluorescence). - Very soft (Mohs 2–2.5) and splits easily into thin plates. - It is radioactive and can be detected with a radiation meter (Geiger counter). - Found with torbernite, uranophane and other secondary uranium minerals. ## Fakes and imitations - Torbernite is also a uranium mineral that forms similar thin square plates; it is emerald green, however, and contains copper instead of calcium; unlike autunite, it does not glow under ultraviolet light. ## What determines its value? Autunite can be used as a uranium ore. Collectors look for vivid yellow-green, large and undamaged groups of plates and specimens that glow strongly under ultraviolet light; specimens from the Autun district in France and the Daybreak mine in the USA are well known. Because it is radioactive and can lose water and deteriorate, it needs careful storage. This information is educational, not buying, selling or investment advice. Value varies enormously with quality and treatment. ## Myths and misconceptions - Myth: Autunite glows in the dark on its own; its radiation makes it shine. Fact: Autunite does not glow by itself; it gives off green-yellow light only under ultraviolet light (fluorescence). Its radioactivity is a separate property and cannot be seen. ## Curious questions **Why does autunite glow under ultraviolet light?** The uranium in autunite's structure absorbs ultraviolet light and gives it back as visible green-yellow light. This is called fluorescence. Autunite is one of the most strongly fluorescent minerals; the glow comes from the ultraviolet light, not from its radioactivity. ## Safety Autunite contains uranium and is radioactive; as uranium decays, radon, a radioactive gas, also forms. According to the World Health Organization, radon is one of the leading causes of lung cancer. Store specimens in a closed, labelled container in a well-ventilated place away from bedrooms, kitchens and living areas, out of reach of children, and open the box in a well-aired space. Do not carry specimens on you, do not hold them longer than necessary and wash your hands after touching them. Because autunite is very soft and crumbly, never break, scrape or grind it: dust that is inhaled or swallowed irradiates the body from inside. ## Did you know? - Autunite loses water in air and turns into meta-autunite. Museums have therefore coated specimens with lacquer to stop them drying out, and storing them in sealed containers is recommended for scientific study. - About half of its weight (48%) is uranium. - The Daybreak mine in Washington State, USA, is known both for fine autunite groups and for producing most of the area's uranium. ## Where is it found? - Autun, Saône-et-Loire, France (Type locality): Autunite was found near Autun in 1852 and named after the town; the Les Oudots quarry is in this district - Daybreak (Dahl) mine, near Mount Spokane, Washington, USA (Known locality): Known for fine autunite groups; most of the area's uranium production came from this mine (coordinate is Mount Spokane) - Sabugal, Guarda, Portugal (Known locality): One of the Portuguese localities the Handbook of Mineralogy cites for autunite ## Sources - [Autunite](https://en.wikipedia.org/wiki/Autunite), Wikipedia - [Handbook of Mineralogy: Autunite](https://www.handbookofmineralogy.org/pdfs/autunite.pdf), Mineralogical Society of America - [Radon and health (fact sheet)](https://www.who.int/news-room/fact-sheets/detail/radon-and-health), World Health Organization - [Torbernite](https://en.wikipedia.org/wiki/Torbernite), Wikipedia - [Autun](https://en.wikipedia.org/wiki/Autun), Wikipedia Source: https://taslar.bumba.tr/en/stones/autunite/ · Licence: CC BY-SA 4.0