Auricupride

Auricupride is a natural alloy that combines copper and gold. Its chemical formula is Cu₃Au. The alloy crystallizes in the cubic crystal system in the L1₂ structure type and occurs as malleable grains or platey masses. It is an opaque yellow with a reddish tint. It has a hardness of 3.5 and a specific gravity of 11.5.^[3]

Auricupride
Auricupride
General
Category	Native elements
Formula	Cu3Au
IMA symbol	Auc[1]
Strunz classification	1.AA.10a
Dana classification	1.1.2.1
Crystal system	Cubic
Crystal class	Hexoctahedral (m3m) H-M symbol: (4/m 3 2/m)
Space group	Pm3m
Identification
Formula mass	387.60 g/mol
Color	Yellow with reddish tint
Fracture	Malleable
Mohs scale hardness	3+1⁄2
Luster	Metallic
Streak	yellow
Diaphaneity	Opaque
Ultraviolet fluorescence	Non-fluorescent
References	[2][3][4][5]

A variant called tetra-auricupride (CuAu) exists. Silver may be present resulting in the variety argentocuproauride (Cu₃(Au,Ag)).^[2]

It was first described in 1950 for an occurrence in the Ural Mountains in Russia. It occurs as low temperature unmixing product in serpentinites and as reduction "halos" in redbed deposits. It is most often found in Chile, Argentina, Tasmania, Russia, Cyprus, Switzerland and South Africa.^[3][2]