Hisingerite

Fe^III₂Si₂O₅(OH)₄ · 2 H₂OIMA symbolHsg^[1]Strunz classification9.ED.10Crystal systemMonoclinic
Unknown space groupUnit cella = 5.4, b = 9.03
c = 14.99 [Å]; β = 98.32°; Z = 4IdentificationColorBlack, brownish-blackCrystal habitMassive, compact; acicular, may be minutely spherical.CleavageNoneFractureConchoidalTenacityBrittleMohs scale hardness2.5 - 3.0LusterVitreous, resinous, greasyStreakYellowish brown, greenDiaphaneityTransparent to translucentSpecific gravity2.43 - 2.67Optical propertiesBiaxial (-)Refractive indexn_α = 1.715 n_γ = 1.730Birefringenceδ = 0.015References^[2][3][4]

Hisingerite is an iron(III) phyllosilicate mineral with formula Fe^III₂Si₂O₅(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.^[2]

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”).^[5] In 1828 it was found at an occurrence in Riddarhyttan, Vastmanland, Sweden. It was named after Wilhelm Hisinger (1766–1852), a Swedish chemist.^[4]

There are also aluminian hisingerite variety in which one of the iron atoms is replaced by aluminium and chrome-alumina-hisingerite variety in which chromium substitutes for iron.^[3]

References