| Thénardite | |
|---|---|
 Thénardite from Sodaville, Nevada | |
| General | |
| Category | Sulfate mineral |
| Formula | Na2SO4 |
| IMA symbol | Thn[1] |
| Strunz classification | 7.AC.25 |
| Crystal system | Orthorhombic |
| Crystal class | Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m) |
| Space group | Fddd |
| Unit cell | a = 5.86 Å, b = 12.3 Å c = 9.82 Å; Z = 8 |
| Identification | |
| Formula mass | 142.04 g/mol |
| Color | White, grayish white, yellowish white, reddish white, brownish white |
| Crystal habit | Forms crust-like prismatic aggregates on matrix |
| Twinning | Interpenetration twinning on {001}; also on {100}; common on {110}; {011} |
| Cleavage | {010} perfect, {101} fair, {100} incomplete |
| Fracture | Splintery, uneven, hackly |
| Tenacity | Brittle |
| Mohs scale hardness | 2.5 |
| Luster | Vitreous to resinous |
| Streak | White |
| Diaphaneity | Transparent |
| Specific gravity | 2.67–2.7, average = 2.68 |
| Optical properties | Biaxial (+) |
| Refractive index | nα = 1.471, nβ = 1.477, nγ = 1.484 |
| Birefringence | δ = 0.013 |
| Pleochroism | none |
| 2V angle | 83° |
| Ultravioletfluorescence | Fluorescent and phosphorescent: short UV=bright white, long UV=yellow-green |
| Solubility | Soluble in water |
| Other characteristics | Salty taste |
| References | [2][3][4] |
Thénardite is an anhydroussodium sulfate mineral, Na2SO4 which occurs in aridevaporite environments, specificallylakes andplayas. It also occurs in drycaves and oldmine workings as an efflorescence and as a crustysublimate deposit aroundfumaroles. It occurs involcanic caves onMount Etna, Italy. It was first described in 1825 for an occurrence in the Espartinas Saltworks inCiempozuelos, Spain, by the Spanish chemist José Luis Casaseca (1800 - 1869). Casaseca named the mineral after his master, the French chemistLouis Jacques Thénard (1777–1857).[3]
Thénardite crystallizes in theorthorhombic system and often forms yellowish, reddish to gray white prismatic crystals although usually in massive crust deposits. Thénardite isfluorescent, white in shortwave and yellow-green in longwaveUV radiation.
In humid conditions, thénardite progressively absorbs water and converts to the deca-hydrated mineralmirabilite, Na2SO4 · 10 H2O.
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