Arcanite is a potassium sulfate mineral with formula K₂SO₄.

Arcanite
Arcanite
General
Category	Sulfate mineral
Formula (repeating unit)	K2SO4
IMA symbol	Acn[1]
Strunz classification	7.AD.05
Crystal system	Orthorhombic
Crystal class	Dipyramidal (mmm) H-M symbol: (2/m 2/m 2/m)
Space group	Pmcn
Unit cell	a = 5.77, b = 10.07 c = 7.48 [Å]; Z = 4
Identification
Color	White to colorless, yellow
Crystal habit	Tabular crystals, typically in crusts and coatings
Twinning	Cyclic on {110}
Cleavage	Good on {010} and {001}
Mohs scale hardness	2
Luster	Vitreous
Streak	White
Diaphaneity	Transparent to translucent
Specific gravity	2.66
Optical properties	Biaxial (+)
Refractive index	nα = 1.494 nβ = 1.495 nγ = 1.497
Birefringence	δ = 0.004
2V angle	Measured: 67°
References	[2][3][4]

Arcanite was first described in 1845 for an occurrence in old pine railroad ties in the Santa Ana tin mine, Trabuco Canyon, Santa Ana Mountains, Orange County, California, US.^[2][4] It has also been reported from hydrothermal deposits in the Cesano geothermal field, Latium, Italy; in bat guano on the Chincha Islands of Peru; and in caves in Western Australia, South Africa and Namibia.^[4]