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Category Mineral
(repeating unit)
Strunz classification 2.EB.15a
Crystal system Orthorhombic
Crystal class Dipyramidal (mmm)
H-M symbol: (2/m 2/m 2/m)
Space group Pnnm
Unit cell a = 4.759 Å, b = 5.797 Å
c = 3.539 Å; Z = 2
Color Tin white with a faint pinkish hue
Crystal habit Rarely as prismatic crystals; commonly massive, granular, radial, fibrous
Twinning On {101}
Cleavage Distinct on {101}
Fracture Irregular
Tenacity Brittle
Mohs scale hardness 5.5-6
Luster Metallic
Streak Grayish black
Diaphaneity Opaque
Specific gravity 7.0-7.1
Optical properties Strongly anisotropic
Pleochroism Weak, yellow to pinkish hue and bluish white
References [1][2][3]

Rammelsbergite is a nickel arsenide mineral with formula NiAs2. It forms metallic silvery to tin white to reddish orthorhombic prismatic crystals, and is usually massive in form. It has a Mohs hardness of 5.5 and a specific gravity of 7.1.

It was first described in 1854 from its type locality in the Schneeberg District in Saxony, Germany. It was named after the German chemist and mineralogist, Karl Friedrich August Rammelsberg (1813–1899).[2]

It occurs as a hydrothermal mineral in medium temperature veins association with skutterudite, safflorite, lollingite, nickeline, native bismuth, native silver, algodonite, domeykite and uraninite.[1]