| Autunite | |
|---|---|
 Autunite from Daybreak Mine, Washington | |
| General | |
| Category | Phosphate minerals |
| Formula | Ca(UO2)2(PO4)2·10–12H2O |
| IMA symbol | Aut[1] |
| Strunz classification | 8.EB.05 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Pnma |
| Unit cell | a = 14.0135(6), b = 20.7121(8), c = 6.9959(3) [Å]; Z = 4 |
| Identification | |
| Formula mass | 986.26 g/mol |
| 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 |
| Twinning | Rare on {110} |
| Cleavage | {001} perfect, {100} and {010} poor |
| Fracture | uneven |
| Mohs scale hardness | 2–2.5 |
| Luster | Vitreous – pearly |
| Streak | Pale yellow |
| Diaphaneity | Transparent to translucent |
| Specific gravity | 3.1–3.2 |
| Density | 3.15 |
| Optical properties | Biaxial (−) |
| Refractive index | nα = 1.553 – 1.555 nβ = 1.575 nγ = 1.577 – 1.578 |
| Birefringence | δ = 0.003 |
| Pleochroism | X = colorless to pale yellow; Y = Z = yellow to dark yellow |
| 2V angle | Measured: 10° to 53° |
| Ultravioletfluorescence | Strong yellow-green fluorescence in UV; Radioactive |
| Solubility | Soluble in acids |
| Alters to | Dehydrates in air |
| Other characteristics | Pseudotetragonal for synthetic material, Radioactive |
| References | [2][3] |
Autunite (hydrated calcium uranyl phosphate), with formula Ca(UO2)2(PO4)2·10–12H2O, is a yellow-greenishfluorescentphosphatemineral with ahardness of 2–2+1⁄2.[4][5] Autunite crystallizes in theorthorhombic system and often occurs as tabular squarecrystals, commonly in small crusts or in fan-like masses. Due to the moderateuranium content of 48.27% it isradioactive and also used as uranium ore. Autunite fluoresces bright green to lime green under UV light. The mineral is also calledcalco-uranite, but this name is rarely used and effectively outdated.[6]
Autunite was discovered in 1852 nearAutun,France, which is also autunite's namesake. It occurs as anoxidation product of uranium minerals ingranitepegmatites andhydrothermal deposits. Associate minerals includemetaautunite,torbernite,phosphuranylite,saleeite,uranophane andsabugalite.[3]
Autunite was named after the town of Autun, France, where the mineral was initially found. The mineral was named by Henry J. Brooke and William H. Miller in 1854.[5] The archaic name "calco-uranite" pairs with the similarly composed mineral,torbernite, which was named "cupro-uranite". Both minerals are named due to their uranium content, with autunite's name referring to its calcium (calco), and torbernite's copper (cupro) quantity.[6]
Researchers found autunite inside the Daybreak Mine onMount Kit Carson,Spokane,Washington (or sometimes referred to as "nearMount Spokane"), in "vugs,fractures, andshear zones ingranitic rock". These areas showed signs of another phosphate,apatite, which may have helped lead to the formation of autunite, by providing a source ofphosphate andlime. The formation may have occurred with the interaction of uranium leached from a separate deposit.[7]
90,000 lbs ofU3O8 were produced from nine properties, although most of the ore came from the Daybreak Mine.[8]
One of the other locations of autunite includes Autun, France, the type locality and namesake of the mineral. The mineral was formed there as analteration ofuraninite and otheruranium bearing minerals.[9] Autunite is also found inCornwall,Saxony, andNorth andSouth Dakota.[10][6]
If the mineral dries out, it can lose its water content and convert to meta-autunite-I, which can turn into meta-autunite-II after heating. These two subsequent minerals are very rare in nature. For scientific studies it is recommended to store the mineral in a sealed container to minimize the water loss. Museums are known to have covered the mineral withlacquer to avoid drying of the mineral.
_France.jpg)
.jpg)
.JPG)
