Autunite

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Autunite
Autunite-69257.jpg
Autunite from Daybreak Mine, Washington
General
Category Phosphate minerals
Formula
(repeating unit)
Ca(UO2)2(PO4)2·10–12H2O
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°
Ultraviolet fluorescence Strong yellow-green fluorescence in UV; Radioactive
Solubility Soluble in acids
Alters to Dehydrates in air
Other characteristics Pseudotetragonal for synthetic material
References [1][2]

Autunite (hydrated calcium uranyl phosphate) with formula: Ca(UO2)2(PO4)2·10–12H2O is a yellow-greenish fluorescent mineral with a hardness of 2–​2 12.[3][4] Autunite crystallizes in the orthorhombic system and often occurs as tabular square crystals. 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 is rarely used.[5]

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.[2]

Etymology[edit]

Autunite was named after the town of Autunite, France, where the mineral was initially found. The mineral was named by Henry J. Brooke and William H. Miller in 1854.[4] The archaic name "calco-uranite" refers to the similar mineral, torbernite, named "cupro-uranite" with calcium instead of copper.[5]

Locations and mining[edit]

Autunite from Mount Kit Carson, Washington

Mount Kit Carson, Washington[edit]

Researchers found autunite inside the Daybreak Mine on Mount Kit Carson, Spokane, Washington (or sometimes referred to as "near Mount Spokane"), in "vugs, fractures, and shear zones in granitic rock". These areas showed signs of another phosphate, apatite, which may have helped lead to the formation of autunite, by providing a source of phosphate and lime. The formation my have occurred with the interaction of uranium leeched from a separate deposit.[6]

90,000 lbs of U3O8 were produced from nine properties, although most of the ore came from the Daybreak Mine.[7]

Other locations[edit]

One of the other locations of autunite includes Autun, France, the type locality and namesake of the mineral. The mineral was formed there as an alteration of uraninite and other uranium bearing minerals.[8] Autunite is also found in Cornwall, Saxony, and North and South Dakota.[9][5]

Meta-autunite[edit]

If the mineral dries out, it converts 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 with lacquer to avoid drying of the mineral.

Gallery[edit]

References[edit]

  1. ^ Mindat.org
  2. ^ a b Handbook of Mineralogy
  3. ^ Barthelmy, Dave. "Autunite Mineral Data". webmineral.com. Retrieved 2018-01-26. 
  4. ^ a b "Autunite: Autunite mineral information and data". www.mindat.org. Retrieved 2018-04-28. 
  5. ^ a b c "Autunite". 1911 Encyclopædia Britannica. Volume 3. 
  6. ^ G. W. Leo (1960). Autunite from Mt. Spokane, Washington. U.S. Geologic Survey, Menlo Park, California: The American Mineralogist. p. 1. 
  7. ^ USGS
  8. ^ Publishing, D. K. (2012-06-18). Nature Guide: Rocks and Minerals. Penguin. ISBN 9781465403520. 
  9. ^ The Encyclopedia Americana: A Library of Universal Knowledge. Encyclopedia Americana Corporation. 1918.