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Formula: Ca(UO2)2(PO4)2.10-12H2
Hydrated phosphate, autunite group,
uranyl mineral
Epitaxial mineral: torbernite
Crystal System: Orthorhombic
Specific gravity: 3.2
Hardness: 2 to 2½
Streak: White to yellowish
Colour: Yellow, greenish yellow, pale green, dark green, greenish black
Luminescence: Strong yellow-green fluorescence under long wave and short wave UV
Solubility: Autunite is moderately soluble in hydrochloric, sulphuric and nitric acid
Common impurities: Ba,Mg
RADIOACTIVE
Environments:
Pegmatites
Hydrothermal environments
Autunite is a secondary mineral found chiefly in the
zone of oxidation and
weathering derived from the alteration of
uraninite or other uranium
minerals in
hypothermal (high temperature) veins. Associated minerals include meta-autunite,
torbernite, phosphuranylite,
saléeite, uranophane,
uranophane-β and sabugalite
(HOM).
Localities
At the Golconda pegmatite field, Governador Valadares, Minas Gerais, Brazil, fine specimens of autunite
have been found, that fluoresce brilliant green under UV, as do all autunite specimens.
Autunite from the Golconda pegmatite field -
Image
The Nanjingqiao U deposit, Pingjiang county, Yueyang, Hunan, China, is an example of
quartz vein-type uranium
mineralisation occurring in the contact zone of a granite
intrusion. Matrix miniatures gathered from the deposit feature typical yellow-green books and sheaves of
autunite crystals in rich coverages over drusy seam linings of
smoky quartz in the
granite matrix
(Minrec 55.1.92).
Autunite from Nanjingqiao - Image
At the type locality, Saint-Symphorien-de-Marmagne, Montcenis, Saône-et-Loire, Bourgogne-Franche-Comté, France,
autunite occurs in
a granite
pegmatite
(Mindat).
Autunite from Saint-Symphorien-de-Marmagne -
Image
At Hagendorf and Pleystein, Bavaria, Germany autunite occurs in
pegmatites
(Dana).
Autunite from Hagendorf - Image
At Johanngeorgenstadt, Erzgebirgskreis, Saxony, Germany, autunite has been identified from the Georg Wagsfort
mine, the Rothe Grube, the Himmelfahrt mine at Steinbach and the Schaar shaft, forming rectangular yellow to greenish
yellow tablets to over 1 cm across. The crystals, probably altered to
meta-autunite after being collected, typically grade into green
torbernite-metatorbernite,
the crystals commonly showing yellow autunite centres grading to green
torbernite edges
(MinRec 55.5.588).
Autunite from Johanngeorgenstadt -
Image
At the Apex Mine, Lander county, Nevada, USA, crystals of autunite to 3 mm have been found covering the surfaces of
quartzite/phyllite
breccias, and small tablets to 2 mm occur locally within open stress fractures in
monzonite. In the finest specimens freestanding crystals to 3 mm occur
in brittle and heavily fractured quartzite clasts caught up locally in fault
breccias. Rarely, two generations of autunite crystallization have been
noted in these clasts. Noteworthy epitactic overgrowths of autunite on torbernite/
metatorbernite have also been noted in a number of specimens
(R&M 87.3.270-276)
Autunite from the Apex mine - Image
At the quarry of the New Hampshire Mica and Mining Company in Alstead, New Hampshire, USA, autunite has been
found in small micaceous
flakes lying between plates of cleavelandite
(AM 13.578-579).
Near Mount Spokane, Spokane county, Washington, USA, autunite is developed in vugs, fractures, and shear zones in
granitic rock. Analyses of the autunite suggest discrete water losses at about
90oC, 145oC, and 220oC. The first water loss probably represents dehydration to
meta-autunite I. The dehydrations at about 145oC and 220oC may involve
interlayer water as in montmorillonite. Unless a saturated atmosphere is maintained,
fully hydrated autunite quickly reverts to meta-autunite I, which is the most stable
form under ordinary conditions of temperature and humidity. Irreversible dehydration from
meta-autunite I to meta-autunite II takes
place at about 80oC
(AM 45.99-128).
Autunite from Mount Spokane - Image
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