Alarsite (AlAsO₄) is an aluminium arsenate mineral with its name derived from its composition: aluminium and arsenate.^[2] It occurs as brittle subhedral grains which exhibit trigonal symmetry. It has a Mohs hardness of 5-5.5 and a specific gravity of 3.32. It is semitransparent, colorless with pale yellow tints and shows a vitreous luster. It is optically uniaxial (+) with refractive indices of n_ω = 1.596 and n_ε = 1.608.

Alarsite
Alarsite crystals found at Tolbachik
General
Category	Mineral
IMA symbol	Ars[1]
Crystal system	trigonal
Crystal class	aluminium arsenate
Space group	P3121 (no. 152) or P3221 (no. 154)
Identification
Colour	colorless with pale yellow tints
Mohs scale hardness	5-5.5
Luster	vitreous luster
Specific gravity	3.32.
Refractive index	nω = 1.596 and nε = 1.608.

It was reported from fumaroles in the Tolbachik volcano, Kamchatka, Far Eastern Region, Russia.^[3][4] It occurs in association with fedotovite, klyuchevskite, lammerite, nabokoite, atlasovite, langbeinite, hematite and tenorite.^[2]