Autunite (Meta-Autunite)
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Autunite is named for the type locality at Autun, Saône-et-Loire, France. Meta-Autunite is a dehydration product of its close cousin, Autunite.

Discovered in 1852 (Autunite), 1904 (Meta-Autunite);
IMA status:  Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

Ca(UO₂)₂(PO₄)₂•6-8(H₂O)

Hydrated Calcium Uranyl Phosphate

Molecular Weight:

986.26 gm

Composition:

Calcium

4.06 %

Ca

5.69 %

CaO

Uranium

48.27 %

U

54.76 %

UO₂

Phosphorus

6.28 %

P

14.39 %

P₂O₅

Hydrogen

2.45 %

H

21.92 %

H₂O

Oxygen

38.93 %

O

100.00 %

100.00 %

= TOTAL OXIDE

Classification

Mineral Classification:

Phosphates

Strunz 8th Ed. ID:

7/E.02-90

Nickel-Strunz 10th Ed. ID:

8.EB.10

8 : PHOSPHATES, ARSENATES, VANADATES
E : Uranyl phosphates and arsenates
B : UO₂:RO₄ = 1:1

Related to:

Meta-Autunite Group. Epitaxial Minerals: Torbernite (oriented growths). Dehydrates in air and alters to Phosphuranylite.

Members of Group:

Meta-Autunite Group: Abernathyite, Bassetite, Chernikovite, Lehnerite, Meta-ankoleite, Meta-autunite, Metaheinrichite, Metakirchheimerite, Metalodèvite, Metanovácekite, Metatorbernite, Metauranocircite, Metauranospinite, Metazuenerite, Natrouranospinite, Sodium Meta-autunite, Uramarsite, Uramphite

Varieties:

None

Synonyms:

Calcium-Autunite, Calcouranite, Lime-Uranite

Crystal Data

Crystallography:

Tetragonal - Ditetragonal Dipyramidal

Crystal Habit:

As thin to moderately thick crystals, tabular on {001} and with rectangular or octagonal outline, to 2 cm; commonly in subparallel growths, foliated or scaly aggregates, and in crusts.

Twinning:

On {110}, interpenetrant, rare.

Physical Properties

Cleavage:

Perfect on {001}; Indistinct on {100}

Fracture:

Conchoidal to Irregular/Uneven

Tenacity:

Brittle

Moh's Hardness:

2.0 - 2.5

Density:

3.05 - 3.20 (g/cm³)  (varies with hydration)

Luminescence:

Fluorescent; Strong yellow-green in SW and LW UV

Radioactivity:

Very Strong; GRapi = 4,234,083.25 (Gamma Ray American Petroleum Institute Units)

Health Warning:

Contains uranium - always wash hands after handling. Avoid inhaling dust when handling or breaking. Never lick or ingest. Avoid prolonged exposure in proximity of the body. Store away from inhabited areas.

Other:

Dehydrates in air. Soluble in acids. Alters to Phosphuranylite.

Optical Properties

Color:

Lemon-Yellow to sulfur-Yellow, Greenish Yellow to pale Green; may be dark Green to Greenish Black

Transparency:

Transparent to Translucent, Opaque

Luster:

Vitreous, Pearly on {001}

Refractive Index:

1.584 - 1.607  Uniaxial ( - ), commonly anomalously Biaxial ( - ), dependent on the H2O content of the crystals.

Birefringence:

0.023

Dispersion:

Strong; r > v

Pleochroism:

Visible. X = colorless to pale yellow; Y = Z = yellow to dark yellow

Occurances

Geological Setting:

Autuinte: A secondary mineral derived from primary uranium-bearing minerals under oxidizing conditions, in hydrothermal veins, granite pegmatites, etc.
Meta-Autunite: A dehydration product of its close cousin, Autunite.

Common Associations:

Autunite, Meta-Autunite, Torbernite, Phosphuranylite, Saléeite, Uranophane, Uranophane-beta, Sabugalite

Common Impurities:

Ba, Mg

Autunite Type Locality:
Meta-Autunite Type Locality:

Saint-Symphorien-de-Marmagne, Montcenis, Saône-et-Loire, Burgundy, France
Daybreak Mine (Dahl lease), Mount Kit Carson, Spokane County, Washington, USA

Year Discovered:

1852 (Autunite); 1904 (Meta-Autunite)

View mineral photos:

Meta-Autunite Mineral Photos and Locations

More Information

Mindat.org 
Webmineral.com

Meta-Autunite is a dehydration product of its close cousin, Autunite. When the mineral Autunite loses water and converts to Meta-Autunite, it becomes what is known as a pseudomorph. A pseudomorph is generally an atom by atom replacement of one mineral's chemistry in place of another mineral's chemistry, while the original crystal's outward shape remains largely unchanged. The process leaves the crystal shape of the original mineral intact, but the original mineral is no longer there. Pseudomorph translated from latin means false shape (pseudo=false; morph=shape). Meta-Autunite is the more stable form of the two and most specimens of Autunite are probably actually Meta-Autunite.

Meta-Autunite is a highly fluorescent mineral. Uranium is the fluorescent activator in Meta-Autunite and Autunite. Remember, because of the uranium, Meta-Autunite and Autunite are a radioactive minerals and should be stored away from other minerals that are affected by radioactivity and human exposure should always be limited. Autunite and Meta-Autunite are two of the more attractive and popular radioactive minerals.

Distribution of Autunite and Meta-Autunite is widespread, with many minor localities, but few for outstanding specimens. In France, at L’Ouche d’Jau, Saint-Symphorien-de-Marmagne, and the Les Oudots mine, Autun district, Saône-et-Loire; from the Margnac mine, Compreignac, Haute-Vienne; large crystals from the Gagnol mine, Lachaux, Puy-de-Dôme. From Sabugal, Urgeiri¸ca, and elsewhere in Portugal. At Peveragno, near Cúneo, Piedmont, Italy. Large crystals from Bergen, Vogtland, Germany. From a number of localities in Cornwall, England. Fine groups from the Daybreak mine, near Mt. Spokane, east of Elk, Spokane County, Washington, USA. At Malacacheta, Minas Gerais, Brazil. Large crystals from Mt. Painter, Flinders Ranges, South Australia.
 

  
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