Meta-Autunite
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.
| 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 |
| 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. |
| 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. |
| 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 |
