Radioactive Autunite Crystals

Autunite is a product of the alteration of uraninite. It is the most common surface uranium mineral, abundant in the oxidation zones of uranium deposits ; it is also found more rarely in pegmatitic veins containing uranium and in some hydrothermal veins.

Autunite crystallizes in the orthorhombic system and often occurs as tabular square crystals, commonly in small crusts or in fan-like masses. Due to the moderate uranium content of 48.27% it is radioactive and also used as uranium ore. Autunite fluoresces bright green to lime green under UV light. The mineral is also called calco-uranite, but this name is rarely used and effectively outdated.

Autunite Radioactive Mineral. Unique Autunite (Meta-Autunite) from Golconda pegmatite district, Brazil. Photo: Thomas Spann

Autunite is a radioactive orthorhombic mineral which results from the hydrothermal alteration of uranium minerals. Used as a uranium ore, it was first discovered in France in 1852.

 The crystals have the shape of thin plates with very nearly square outline (89° 17′ instead of 90°). An important character is the perfect micaceous cleavage parallel to the basal plane, on which plane the lustre is pearly.

The colour is sulphur-yellow, and this enables the mineral to be distinguished at a glance from the emerald-green torbernite. Hardness 2-2½; specific gravity 3.05-3.19. Autunite is usually found with pitchblende and other uranium minerals, or with ores of silver, tin and iron; it sometimes coats joint-planes in gneiss and pegmatite.

Autunite is a radioactive mineral and can be harmful to human health. The radiation from autunite can cause cancer and other health problems. It is important to handle autunite with care and to avoid exposure to its radiation.

Properties of Autunite:

Chemical Formula: Ca(UO₂)₂(PO₄)₂·10–12H₂O
Crystal system: Orthorhombic
Color: Lemon-yellow to sulfur-yellow, greenish yellow to pale green; may be dark green to greenish black
Crystal habit: Tabular crystals, foliated or scaly aggregates, and in crusts
Occurrence: A secondary mineral derived from primary uranium-bearing minerals under.

It is a radioactive mineral that reacts very strongly to UV with a very characteristic green fluorescence. Autunite is an important uranium ore. It is also popular with collectors.

Autunite Radioactive Mineral. Photo Copyright: Enrico Bonacina

Associated Minerals are torbernite, meta-torbernite, uranocircite, uranophane, uraninite and other uranium minerals.
Other Characteristics: fluorescent yellow-green, radioactive, somewhat pleochroic and thin crystals or cleavage sheets are bendable.
Notable Occurences include Autun, France; Cornwall, England; Mitchell Co., North Carolina and Mt. Spokane, Washington, USA; Zaire; Bergen, Germany and Portugal.
Best Field Indicators are color, crystal habit, fluorescence, radioactivity, associations and flexible crystals.