Hercynite

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Hercynite
Hercynite.jpg
General
Category Oxide minerals
Spinel group
Spinel structural group
Formula
(repeating unit)
Fe2+Al2O4
Strunz classification 04.BB.05
Identification
Formula mass 173.81
Color Black
Crystal habit Euhedral crystals. Also massive to granular
Crystal system Isometric (4/m 3 2/m) Space Group: F d3m
Cleavage [111] indistinct
Fracture Uneven - flat surfaces (not cleavage) fractured in an uneven pattern.
Mohs scale hardness 7.5
Luster Vitreous (glassy)
Streak dark green
Specific gravity 3.95
Optical properties Isotropic
Refractive index n=1.8
Other characteristics non-radioactive
References [1][2][3]

Hercynite is a spinel mineral with the formula FeAl2O4.

It occurs in high-grade metamorphosed iron rich argillaceous sediments as well as in mafic and ultramafic igneous rocks. Due to its hardness it also is found in placers.[1]

It was first described in 1847 and its name originates from the Latin name for the Harz, Silva Hercynia, where the species was first found.[1][2]

References[edit]