Arsenolite

Arsenolite is an arsenic mineral, chemical formula As₂O₃. 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.^[2]

Arsenolite
Arsenolite from the White Caps Mine, Manhattan District, Nye County, Nevada (size: 6.0 x 4.3 x 2.9 cm)
General
Category	Oxide mineral
Formula	As2O3
IMA symbol	Aso[1]
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
Identification
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	[2][3][4]

Arsenolite belongs to the minerals which are highly toxic.^[4]

Occurrence

It was first described in 1854 for an occurrence in the St Andreasberg District, Harz Mountains, Lower Saxony, Germany.^[4]

It occurs by the oxidation of arsenic-bearing sulfides in hydrothermal veins. It also occurs as a result of mine or coal seam fires.^[2]