alacránite

{{Infobox mineral | name = Alacranite | category = Sulfide mineral | boxwidth = | boxbgcolor = | image = Alacránit, Radvamice, detail.jpg | imagesize = | caption = Alacránite from former Kateřina Mine, Radvanice, Trutnov District, Czech Republic (1999) | formula = As8S9 |IMAsymbol=Acr | molweight = | strunz = 2.FA.20 | system = Monoclinic | class = Prismatic (2/m) (same H-M symbol) | symmetry = P2/c | unit cell = a = 9.942, b = 9.601 c = 9.178 [Å]; β = 101.94°; Z = 2 | color = Orange to pale gray, rose-yellow internal reflections | habit = Equant grains | twinning = | cleavage = Imperfect on {100} | fracture = | tenacity = Brittle | mohs = 1.5 | luster = Vitreous, resinous, greasy | polish = | refractive = nα = 2.390(1) nγ = 2.520(2) | opticalprop = Biaxial (+) | birefringence = 0.1300 | dispersion = | pleochroism = | fluorescence = | absorption = | streak = Yellow-orange | gravity = 3.4 - 3.46 | density = | diagnostic = | solubility = | diaphaneity = Transparent to translucent | other = | references = }}

Alacránite (As8S9) is an arsenic sulfide mineral first discovered in the Uzon caldera, Kamchatka, Russia. It was named for its occurrence in the Alacrán silver/arsenic/antimony mine. Pampa Larga, Chile. It is generally more rare than realgar and orpiment. Its origin is hydrothermal. It occurs as subhedral to euhedral tabular orange to pale gray crystals that are transparent to translucent. It has a yellow-orange streak with a hardness of 1.5. It crystallizes in the monoclinic crystal system. It occurs with realgar and uzonite as flattened and prismatic grains up to 0.5 mm across.