hisingerite

{{infobox mineral | name = Hisingerite | image = Hisingerite-282352.jpg | alt = | caption = Crystallized plates of reddish-brown, silver metallic-lustre hisingerite crystals | category = Phyllosilicate minerals | formula = {{chem2|Fe^{III}2Si2O5(OH)4 * 2 H2O}} | IMAsymbol = Hsg | molweight = | strunz = 9.ED.10 | dana = | system = Monoclinic Unknown space group | class = | symmetry = | unit cell = a = 5.4, b = 9.03 c = 14.99 [Å]; β = 98.32°; Z = 4 | color = Black, brownish-black | colour = | habit = Massive, compact; acicular, may be minutely spherical. | twinning = | cleavage = None | fracture = Conchoidal | tenacity = Brittle | mohs = 2.5 - 3.0 | luster = Vitreous, resinous, greasy | streak = Yellowish brown, green | diaphaneity = Transparent to translucent | gravity = 2.43 - 2.67 | density = | polish = | opticalprop = Biaxial (-) | refractive = nα = 1.715 nγ = 1.730 | birefringence = δ = 0.015 | pleochroism = | 2V = | dispersion = | extinction = | length fast/slow = | fluorescence = | absorption = | melt = | fusibility = | diagnostic = | solubility = | impurities = | alteration = | other = | prop1 = | prop1text = |references = }} Hisingerite is an iron(III) phyllosilicate mineral with formula {{chem2|Fe^{III}2Si2O5(OH)4 * 2 H2O}}. A black or dark brown, lustrous secondary mineral, it is formed by the weathering or hydrothermal alteration of other iron silicate and sulfide minerals.

It was first described in 1751 by A.F. Cronstedt from Väster Silvberg, Dalarna, Sweden (under the name “kolspeglande järnmalm”), and in 1810 by W. Hisinger from the Gillinge iron mine, Södermanland, Sweden (“svart stenart”, later “gillingit”). In 1828 it was found at an occurrence in Riddarhyttan, Vastmanland, Sweden. It was named after Wilhelm Hisinger (1766–1852), a Swedish chemist.