Autunite

Autunite
Autunite from Daybreak Mine, Washington
General
CategoryPhosphate minerals
Formula
(repeating unit)
Ca(UO2)2(PO4)2·10–12H2O
IMA symbolAut[1]
Strunz classification8.EB.05
Crystal systemOrthorhombic
Crystal classDipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space groupPnma
Unit cella = 14.0135(6),
b = 20.7121(8),
c = 6.9959(3) [Å]; Z = 4
Identification
Formula mass986.26 g/mol
ColorLemon-yellow to sulfur-yellow, greenish yellow to pale green; may be dark green to greenish black
Crystal habitTabular crystals, foliated or scaly aggregates, and in crusts
TwinningRare on {110}
Cleavage{001} perfect, {100} and {010} poor
Fractureuneven
Mohs scale hardness2–2.5
LusterVitreous – pearly
StreakPale yellow
DiaphaneityTransparent to translucent
Specific gravity3.1–3.2
Density3.15
Optical propertiesBiaxial (−)
Refractive indexnα = 1.553 – 1.555 nβ = 1.575 nγ = 1.577 – 1.578
Birefringenceδ = 0.003
PleochroismX = colorless to pale yellow; Y = Z = yellow to dark yellow
2V angleMeasured: 10° to 53°
Ultraviolet fluorescenceStrong yellow-green fluorescence in UV; Radioactive
SolubilitySoluble in acids
Alters toDehydrates in air
Other characteristicsPseudotetragonal for synthetic material, Radioactive
References[2][3]

Autunite (hydrated calcium uranyl phosphate), with formula Ca(UO2)2(PO4)2·10–12H2O, is a yellow-greenish fluorescent phosphate mineral with a hardness of 2–2+12.[4][5] 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 The mineral is also called calco-uranite, but this name is rarely used and effectively outdated.[6]

Autunite was discovered in 1852 near Autun, France, which is also autunite's namesake. It occurs as an oxidation product of uranium minerals in granite pegmatites and hydrothermal deposits. Associate minerals include metaautunite, torbernite, phosphuranylite, saleeite, uranophane and sabugalite.[3]

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Mindat.org
  3. ^ a b Handbook of Mineralogy
  4. ^ Barthelmy, Dave. "Autunite Mineral Data". webmineral.com. Retrieved 2018-01-26.
  5. ^ "Autunite: Autunite mineral information and data". www.mindat.org. Retrieved 2018-04-28.
  6. ^ "Autunite" . Encyclopædia Britannica. Vol. 03 (11th ed.). 1911.