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.

Rammelsbergite
General
Category	Mineral
Formula (repeating unit)	NiAs2
IMA symbol	Rmb[1]
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
Identification
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	[2][3][4]

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).^[3]

It occurs as a hydrothermal mineral in medium temperature veins association with skutterudite, safflorite, lollingite, nickeline, native bismuth, native silver, algodonite, domeykite and uraninite.^[2]