Plášilite
Very rare uranium mineral
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Plášilite is a very rare uranium mineral with the formula Na2(UO2)(SO4)2•3H2O.[2][3] Chemically related minerals include natrozippeite, belakovskiite, meisserite, fermiite and oppenheimerite.[4][5][6][7][8] Most of these uranyl sulfate minerals were originally found in the Blue Lizard mine, San Juan County, Utah, US.[9] The mineral is named after Czech crystallographer Jakub Plášil.[3]
| Plášilite | |
|---|---|
| General | |
| Category | Sulfate mineral |
| Formula | Na(UO2)(SO4)(OH)•2H2O |
| IMA symbol | Pšl[1] |
| Crystal system | Monoclinic |
| Crystal class | Prismatic (2/m) (same H-M symbol) |
| Space group | P21/c |
| Unit cell | a = 8.71, b = 13.84, c = 7.05 [Å], β = 112.13° (approximated) |
| Identification | |
| Color | Greenish yellow |
| Crystal habit | prismatic |
| Cleavage | {010} and {001}, perfect |
| Tenacity | Brittle |
| Mohs scale hardness | 2-3 |
| Luster | Vitreous |
| Streak | White |
| Diaphaneity | Transparent |
| Density | 3.73 (calculated) (approximated) |
| Optical properties | Biaxal (+) |
| Refractive index | nα=1.56, nβ=1.58, nγ=1.61 (approximated) |
| Pleochroism | ~Colourless (X), very pale yellow (Y), pale yellow (Z) |
| 2V angle | 88o (measured) |
| Ultraviolet fluorescence | Bluish-white |
| Other characteristics |  Radioactive |
| References | [2][3] |
Association and origin
Plášilite is associated with other sulfate minerals: natrozippeite, johannite, blödite, brochantite, chalcanthite, gypsum, hexahydrite, manganoblödite, and tamarugite. Non-sulfate coexisting minerals include atacamite, calcite, dickite and gerhardtite. Plášilite is secondary in origin, being the product of weathering of the primary uranium mineral, uraninite.[2]
Crystal structure
The crystal structure of plášilite is of a new type. Its building blocks are:[2]
- (UO2)2(SO4)2(OH)2 sheets, with a charge 2-, parallel to (010), of a phosphuranylite topology
- edge-sharing NaO2(H2O)4 polyhedra, parallel to [001]
The sodium-bearing polyhedra link the uranyl-sulfate sheets. It terms of sheet geometry, crystal structure of plášilite is similar to that of deliensite.[2]