Atheneite

Atheneite
General
Category	Arsenide mineral
Formula (repeating unit)	(Pd,Hg)3As
Strunz classification	2.AC.05a
Crystal system	Hexagonal
Crystal class	Ditrigonal dipyramidal (6m2) H-M symbol: (6m2)
Space group	P62m
Unit cell	a = 6.813, c = 3.4892 [Å]; Z = 3
Identification
Color	Gray to gray white; white with bluish tint in reflected light
Crystal habit	Irregular blebs, inclusions
Luster	Metallic
Diaphaneity	Opaque
Specific gravity	10.2
Pleochroism	Very weak, in pale yellow to pale bluish gray
References

Atheneite is a rare palladium, mercury arsenide mineral with formula (Pd,Hg)₃As associated with palladium–gold deposits. Its composition parallels that of arsenopalladinite (Pd₈(As,Sb)₃), isomertieite (Pd₁₁Sb₂As₂) and meritieite-II (Pd₈(Sb,As)₃)(Cabral, 2002).

Discovery and occurrence

It was discovered in 1974 by A.M. Clark, A.J. Criddle, and E.E. Fejer in the Minas Gerais mine in the town of Itabira, Brazil (Clark, 1974). Atheneite was also found in 1982 during a major gold rush at Serra Pelada in northern Brazil. Since then it has been found in the northern region of Para, Brazil, the northern region of Russia, and the Limpopo province of South Africa (Cabral, 2002; Trabaev, 1995). Its name is derived from the Greek goddess Pallas Athena for its association with palladium-gold deposits. It was first found in concentrates from gold washings in Brazil with intergrowths of arsenopalladinite (Fleischer, 1974). Hematite was also found in intergrowths with atheneite, and is interpreted as being the product of a low temperature, hydrothermal origin.

Structure

Atheneite crystallizes in the hexagonal crystal system with space group P62m and a point grouping of 6m2. It has a ditrigonal dipyramidal crystal form. This mineral does not extinguish under crossed polars, showing bright anisotropic colors from purple-brown to dark grey (Fleischer, 1974). These birefringence colors are of the first order. The atomic structure of atheneite is very similar to that of the hexagonal structure carbons that make up graphite.

Physical properties

Atheneite has a metallic luster and its color ranges from white/gray to blue/gray tint. Its Mohs hardness scale is 4.5-5. The Vickers hardness test puts this mineral at a 48. Atheneite also has a specific gravity of 10.2. When placed in a reflected light, it gives off a white light with a yellowish hue and shows very weak reflectance pleochroism in oil (Fleischer, 1974).

References

• New mineral names, Fleischer, Michael In: American Mineralogist, 1974, vol. 59, Issue 11-12, pp 1330–1332.
• Palladium and Platinum Minerals From the Serra Pelada Au-Pd-Pt Deposit, Carajas Mineral Province, Northern Brazil, Cabral, Alexandre Raphael; Lehmann, Bernd; Dwitdo-Ribeiro, Ribeiro; Cravo Costa; Henrique, Carlos: The Canadian Mineralogist, 2002, vol. 40, pp1451–1463.
• Palladium Gold and Palladium Arsenide-Antimonide Minerals from Congo Soco Iron Ored Mine, Quadrilatero Ferritero, Minas Gerais Brazil, Cabral, A.R.: Kwitko, R: Jones R.D. Applied earth science, vol.111, num. 1, April 2002, pp. 74–80.
• Palladium arsenide-antimonides from Itabira, Minas Gerais, Brazil, Clark, A. M. In: Mineralogical Magazine and Journal of the Mineralogical Society, 1974, Vol. 39, Issue 305, pp. 528–543
• New Gold-Palladium Type of Mineralization in the Kozhim Region of Circumpolar Ural (Russia). Trabaev, M.B.; Kuznetsov, S.K.; Moralev, G.V.; Soboleva, A.A.; Laputina, I.P. Geology of Ore Deposits, 1995.