Thenardite

Thenardite
Sodaville, Mineral County, Nevada
General
Category	Sulfate mineral
Chemical formula	Na2SO4
Strunz classification	07.AC.25
Identification
Molar mass	142.04
Color	White, grayish white, yellowish white, reddish white, brownish white
Crystal habit	Forms crust-like prismatic aggregates on matrix
Crystal system	Orthorhombic (2/m 2/m 2/m), Space group Fddd
Twinning	Interpenetration twinning on {001}; also on {100}
Cleavage	{010} Perfect
Fracture	Splintery
Mohs scale hardness	2.5
Luster	Vitreous
Streak	White
Diaphaneity	Transparent
Specific gravity	2.67–2.7, average = 2.68
Optical properties	Biaxial (+), 2V=83°
Refractive index	nα = 1.471, nβ = 1.477, nγ = 1.484
Birefringence	δ = 0.013
Pleochroism	none
Other characteristics	Not radioactive, non-magnetic. Fluorescent and phosphorescent: short UV=bright white, long UV=bright white
References

Thenardite is an anhydrous sodium sulfate mineral, Na₂SO₄ which occurs in arid evaporite environments. It also occurs in dry caves and old mine workings as an efflorescence and as a crusty deposit around fumaroles. It occurs in volcanic caves on Mt. Etna, Italy and was named after the French chemist, Louis Jacques Thénard (1777–1826).

Thenardite crystallizes in the orthorhombic system and often forms yellowish, reddish to grey white prismatic crystals although usually in massive crust deposits. Thenardite is fluorescent, white in shortwave and yellow-green in longwave UV radiation.

In humid conditions, thenardite gradually absorbs water and converts to the mineral mirabilite, Na₂SO₄·10H₂O.