Atheneite

Atheneite is a rare metallic compound commonly associated with palladium–gold deposits. 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).

Atheneite has a chemical structure very similar to that of graphite. Its hexagonal crystal system contributes to its metallic luster, and its color is indicative of its chemical makeup ((Pd,Hg)₃As). Its name is derived from the Greek goddess Pallas Athena for its association with palladium-gold deposits. Not much is known about Atheneite because of its rarity.
Composition and Geologic Occurrence

Atheneite has the chemical formula of (Pd,Hg)₃As which gives it the nomenclature of a palladium arsenide in an arsenic grouping. This mineral’s composition parallels that of arsenopalladinite Pd₈(As, Sb)₃, isomertieite, Pd₁₁Sb₂As₂2, and meritieite-II (Cabral, 2002). According to the American Mineralogist, the mineral was first found in concentrates from gold washings in Brazil with intergrowths of arsenopalladinite (Fleisher, 1974). Iron rich hematite was also found in intergrowths with atheneite, and is interpreted as being the product of a low temperature, hydrothermal origin.

Structure

Atheneite’s space group is P6/mmm. It also has a point grouping of 6/m 2/m 2/m which concludes that its crystal system is hexagonal. Atheneite actually has a dihexagonal dipyramidal crystal form. This same complex hexagonal structure is also the structural make up of graphite. 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, however, the bonds that hold the atoms together in atheneite are much stronger than those of graphite.

Physical Properties

Atheneite, as the derivation of the name suggests, has a metallic luster like that of gold. The color ranges from white/grey to blue/grey tint. Its Mohs hardness scale is 4.5-5. The absolute hardness scale puts this mineral at a 48. Atheneite also has a density of 10.2 g/cm³. 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 Minerologist, 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.

List of minerals