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Arsenolite from the White Caps Mine, Manhattan District, Nye County, Nevada (size: 6.0 x 4.3 x 2.9 cm)
Category Oxide mineral
(repeating unit)
Strunz classification 4.CB.50
Crystal system Cubic
Crystal class Hexoctahedral (m3m)
H-M symbol: (4/m 3 2/m)
Space group Fd3m
Unit cell a = 11.074 Å; Z = 16
Formula mass 197.841 g/mol
Color White, pale blue, pink to pale yellow if impure
Crystal habit Common as tiny octahedra; aggregates or crusts; botryoidal, stalactitic
Cleavage On {111}
Fracture Conchoidal
Mohs scale hardness 1.5
Luster Vitreous to silky; may be earthy or dull
Streak white /pale white
Diaphaneity Transparent
Specific gravity 3.87
Optical properties Isotropic; may be anomalously anisotropic
Refractive index n = 1.755
Other characteristics Astringent, sweetish taste; toxic
References [1][2][3]

Arsenolite is an arsenic mineral, chemical formula As4O6. It is formed as an oxidation product of arsenic sulfides. Commonly found as small octahedra it is white, but impurities of realgar or orpiment may give it a pink or yellow hue. It can be associated with its dimorph claudetite (a monoclinic form of As2O3) as well as realgar (As4S4), orpiment (As2S3) and erythrite, Co3(AsO4)2·8H2O.[1]

Arsenolite belongs to the minerals which are highly toxic.[3]


It was first described in 1854 for an occurrence in the St Andreasberg District, Harz Mountains, Lower Saxony, Germany.[3]

It occurs by the oxidation of arsenic-bearing sulfides in hydrothermal veins. It also occurs as a result of mine or coal seam fires.[1]