Autunite
Autunite, the calcium uranyl phosphate: tetragonal, hardness 2 to 2.5, density 3.05 to 3.2 with hydration, yellow-green in UV. Its water ledger and localities.
Autunite is a calcium uranyl phosphate, Ca(UO2)2(PO4)2(H2O)11 on the IMA list (G, 1852, France): tetragonal yellow to green plates to 2 cm, hardness 2 to 2.5, density 3.05 to 3.2 with hydration, strong yellow-green fluorescence. Its water count is not fixed: the IMA writes 11, the Handbook 10 to 12, and its calculated density uses 10.5.
In short
- The species. The Handbook of Mineralogy sheet gives a tetragonal autunite-group mineral in thin to moderately thick plates tabular on {001}, rectangular or octagonal, to 2 cm; perfect {001} cleavage; hardness 2 to 2.5; lemon-yellow to pale green, may be dark green to greenish black; streak pale yellow. The September 2026 IMA-CNMNC Master List writes Ca(UO2)2(PO4)2(H2O)11, status G, 1852, France.
- The water ledger. One species, four water counts: 11 on the IMA list, 10 to 12 in the Handbook header, 10.5 for the sheet’s calculated density and 12 in its ideal composition column. Worked on standard atomic weights, the 12-water column reproduces exactly: UO3 58.00, P2O5 14.39, CaO 5.69, H2O 21.92 wt%.
- The 3.14 check. Two formula units in the sheet’s cell (1,007.7 Å3) give 3.132 at 10 water, 3.161 at 10.5, 3.191 at 11 and 3.250 at 12. The printed 3.14 is closer to 10 water than to the 10.5 it names, a gap of 0.021; the measured 3.05 to 3.2, which the sheet says varies with hydration, brackets all but the 12-water figure.
- The Autun analysis. The sheet’s analysis from Autun, France, reads UO3 60.84, P2O5 13.40, CaO 5.31, H2O 20.33 wt%. Set to 2 uranium it gives 10.61 water, inside the 10 to 12 range, but only 1.78 phosphorus and 0.89 calcium: 50.63% uranium against 49.17% for the IMA formula.
- Radioactive, on the sheet. The physical-properties line ends “Dehydrates in air. Radioactive.” Hazard questions are not answered here: they are routed to is autunite dangerous and is my mineral radioactive, and nothing on this page is advice.
| Water count | Where it is printed | Formula mass | Uranium by mass | Water by mass | Density from the cell | Printed density |
|---|---|---|---|---|---|---|
| 10 H2O | Handbook header, low end | 950.22 | 50.10% | 18.96% | 3.132 | 3.05–3.2 measured |
| 10.5 H2O | Handbook, D(calc.) | 959.23 | 49.63% | 19.72% | 3.161 | 3.14 calculated |
| 11 H2O | IMA list, September 2026 | 968.24 | 49.17% | 20.47% | 3.191 | 3.05–3.2 measured |
| 12 H2O | Handbook header, high end; ideal column (2) | 986.25 | 48.27% | 21.92% | 3.250 | Above the measured range |
| 10.61 H2O (analysis) | Autun, France, column (1) | — | 50.63% (from UO3 60.84) | 20.33% printed | — | — |
| 6 H2O (meta-autunite) | IMA list: Ca(UO2)2(PO4)2·6H2O, G, 1904, USA | 878.16 | 54.21% | — | Not worked | Not on this sheet |
What is autunite? The calcium uranyl phosphate
Autunite is the calcium member of the uranyl phosphates: calcium, two uranyl groups, two phosphates and water. The Handbook of Mineralogy autunite sheet gives a tetragonal mineral, point group 4/m 2/m 2/m, space group I4/mmm, a 6.989, c 20.63 Å, Z 2, in the autunite group. Crystals are thin to moderately thick, tabular on {001}, with rectangular or octagonal outline, to 2 cm; it is common in subparallel growths, foliated or scaly aggregates and crusts. Twinning on {110}, interpenetrant, is rare.
Physical and optical properties. Cleavage perfect on {001}, indistinct on {100}; hardness 2 to 2.5; measured density 3.05 to 3.2, which the sheet says varies with hydration. Lemon-yellow to sulfur-yellow, greenish yellow to pale green, and it may be dark green to greenish black; streak pale yellow; lustre vitreous, pearly on {001}. Uniaxial (−), commonly anomalously biaxial (−), ω 1.575 and ε 1.572 (ε read from the rendered sheet), α 1.553 to 1.555, β 1.575, γ 1.577 to 1.578, 2V 10° to 53°; pleochroism X colourless to pale yellow, Y = Z yellow to dark yellow; dispersion r > v, strong.
Three short sentences. The same line ends “Strong yellow-green fluorescence in UV. Dehydrates in air. Radioactive.” Background on the glow is on fluorescent minerals explained; lamp exposure limits are in the ICNIRP 2004 guidelines on limits of exposure to ultraviolet radiation, and this page gives no lamp advice. The sheet calls autunite a secondary mineral derived from primary uranium-bearing minerals under oxidizing conditions, in hydrothermal veins and granite pegmatites, with meta-autunite, torbernite, phosphuranylite, saléeite, uranophane, uranophane-beta and sabugalite.
How much water is in autunite? The 3.14 check
Between 10 and 12 waters on the Handbook, 11 on the IMA list, and the printed density fits about 10. The September 2026 IMA list writes Ca(UO2)2(PO4)2(H2O)11. The Handbook header writes ·10–12H2O, its calculated density 3.14 is labelled “for 10.5H2O”, and its ideal column (2) is Ca(UO2)2(PO4)2·12H2O. Worked on standard atomic weights, the 12-water formula weighs 986.25 and is UO3 58.00, P2O5 14.39, CaO 5.69 and H2O 21.92 wt%: column (2) to the hundredth.
The cell. A tetragonal cell is a²c: 6.989² × 20.63 = 1,007.7 Å3. Two formula units in it give 3.132 g/cm3 at 10 water, 3.161 at 10.5, 3.191 at 11 and 3.250 at 12. So the printed 3.14 does not reproduce at the 10.5 it names: it is 0.021 low, and closer to the 10-water figure. Holding the cell fixed is itself an approximation, since a crystal losing water does not keep its cell, so this is a check on the sheet’s arithmetic, not a way to count water in a specimen. The measured 3.05 to 3.2 covers the 10, 10.5 and 11 figures.
Documented failure: the Autun analysis. Column (1), from Autun, reads UO3 60.84, P2O5 13.40, CaO 5.31 and H2O 20.33, total 99.88. Normalised to 2 uranium it gives 10.61 water, inside the 10 to 12 range, but 1.78 phosphorus and 0.89 calcium where the formula has 2 and 1. The analysed material is uranium-rich against the formula, 50.63% uranium against 49.17%, and the sheet does not say why; this page does not guess.
Autunite, meta-autunite and torbernite: what the lists print
Three rows on the IMA list contain the word autunite: autunite, meta-autunite and metanatroautunite. The list writes meta-autunite Ca(UO2)2(PO4)2·6H2O, status G, 1904, USA; worked, that is 54.21% uranium by mass against autunite’s 49.17%, because what differs is water. The autunite sheet names meta-autunite first among its associates and says only “Dehydrates in air”; the conversion, the volume change and what follows from them are set out on is autunite dangerous, whose figures this page agrees with and does not repeat. The general idea of a crystal keeping its outline while its species changes is on what is a pseudomorph.
Torbernite is the copper analogue. The IMA list writes torbernite Cu(UO2)2(PO4)2(H2O)4·8H2O and metatorbernite Cu(UO2)2(PO4)2(H2O)4·4H2O: copper where autunite has calcium. The autunite sheet allows dark green to greenish black among its colours, so colour alone does not separate a dark autunite from a torbernite; the fluorescence and chemistry route is set out on the torbernite page and on is torbernite radioactive, and is not repeated here.
Is autunite a uranium ore? The sheet calls it a secondary mineral derived from primary uranium-bearing minerals; it does not call it an ore, and no fetched source used here does, so this page makes no ore claim. The uranium content is a chemistry number, worked above; what it means for a collection is a hazard question, routed to is my mineral radioactive, and nothing here is advice. The difference between a uranium mineral and the element is on is uraninite the same as uranium.
Where is autunite found? The Distribution field
“Widespread, many minor localities, but few for outstanding specimens.” That is the sheet’s own opening. In France it lists L’Ouche d’Jau, Saint-Symphorien-de-Marmagne, and the Les Oudots mine, Autun district, Saône-et-Loire; the Margnac mine, Compreignac, Haute-Vienne; and large crystals from the Gagnol mine, Lachaux, Puy-de-Dôme. From Sabugal, Urgeiriça and elsewhere in Portugal; at Peveragno, near Cúneo, Piedmont, Italy; large crystals from Bergen, Vogtland, Germany; and from a number of localities in Cornwall, England.
Outside Europe. Fine groups from the Dahl (Daybreak) mine, near Mt. Spokane, east of Elk, Spokane Co., Washington, USA; at Malacacheta, Minas Gerais, Brazil; and large crystals from Mt. Painter, Flinders Ranges, South Australia. The X-ray powder pattern on the sheet is from the Les Oudots mine.
Name and type material. The name is for Autun, France, near to which the first specimens to be analysed were collected; type material is at the Natural History Museum, Paris, H6307, and the IMA list gives 1852 and France. The sheet marks no type locality, and this page does not supply one; the term is explained on what is a type locality. More uranium and phosphate species are in the species index. We hold no catalogue and nothing here is offered for sale; the wanted list is the only commercial route.