Sperrylite

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Sperrylite
Category Mineral
Chemical formula PtAs2
Identification
Color tin white
Crystal habit well-formed finely crystalline, massive to reniform
Crystal system cubic
Cleavage cubic indistinct
Fracture conchoidal
Mohs Scale hardness 6 - 7
Luster metallic
Streak black
Specific gravity 10.6

Sperrylite is a platinum arsenide mineral with formula: PtAs2 and is an opaque metallic tin white mineral which crystallizes in the isometric system with the pyrite group structure. It forms cubic, octahedral or pyritohedral crystals in addition to massive and reniform habits. It has a Mohs hardness of 6 - 7 and a very high specific gravity of 10.6.

It was discovered by Francis Louis Sperry, an American chemist, in 1889 at Sudbury.

The most important occurrence of Sperrylite is in the nickel ore deposit of Sudbury Basin in Ontario, Canada. It also occurs in the layered igneous complex of the Bushveld region of South Africa and the Oktyabr'skoye copper-nickel deposit of the Eastern-Siberian Region, Russia.

Contents

[edit] Geologic occurrence

Sperrylite is the most common platinum mineral, it generally occurs with a wide array of other unusual minerals, including cooperite [(Pt,Pd,Ni)S], laurite [RuS2], kotulskite [Pd(Te,Bi)], merenskyite [(Pd,Pt)(Te,Bi)2], iridium-osmium (Ir-Os) alloys, sudburyite [(Pd,Ni)Sb], omeiite [(Os,Ru)As2], testibiopalladite [PdTe(Sb,Te)], and niggliite [PtSn], to name a few. It does not readily decompose through normal weathering processes and, consequently, has been reported in widely scattered alluvial deposits. Somewhat surprisingly, the first was as tiny crystals found with rhodolite garnet and corundum during alluvial gem mining in streams draining Mason Mountain, Macon County, North Carolina (Hidden 1898). Sperrylite has been identified in Finland from sulfide deposits generally associated with layered mafic-ultramafic complexes.

[edit] Structure

Sperrylite belongs to the pyrite group of minerals and therefore it shares similar structure and crystal habits with them. Analyses typically show minor amounts of rhodium. trace copper, iron, and antimony as well as intergrowths with Pt-Fe are reported from some occurrences. Sperrylite crystallizes in Pa3, with a =5.9681(l) A. (Szymański, 1979). It has very similar crystal structure as in platarsite [Pt(As,S)2]. Sperrylite crystals vary considerably in shape and size and are usually enclosed in a variety of host minerals. They are usually closely associated with basemetal sulfide. They are commonly at the edge and partially enclosed by pentlandite, pyrrhotite or chalcopyrite. Seabrook (2004). Sperrylite is composed of loose aggregate of bright silver cubes, some with octahedral modifications. The grains are mostly anhedral, but a few euhedral grains could also be encountered. Sperrylite is formed by contact metamorphism, as in indicated by the development of triple point annealing contacts with pyrrhotite grains. The grains of sperrylite are surrounded by later veins of pyrite. Sperrylite is cubic (2/m3) and is typically seen in well-developed cubes or cuboctahedra, some of which are so highly modified that crystal edges and comers appear rounded. (Nicol and Goldschmidt 1903) identified seventeen crystal forms exhibited by sperrylite, including four different trapezohedra, a trisoctahedron, five pyritohedra, and four diploids. Crystals to 2.5 cm have been reported.

Cell dimensions a = 5.967, Z = 4; V = 212.46 Den(Calc)= 10.78
Crystal system Isometric - Diploidal H-M Symbol (2/m 3) Space Group: P a3
X ray diffraction By Intensity(I/Io): 1.801(1), 1.148(0.7), 2.98(0.6)
Forms [1 0 2] [1 1 1] [1 0 0]

[edit] Physical properties

Sperrylite is a tin-white mineral known for its brilliant metallic luster, with a grey to black streak. It has indistinct cleavage on {001} and a conchoidal fracture and is brittle. Its hardness is between 6 and 7, and it is quite dense with a calculated specific gravity of 10.78. It has an isometric cystal system, Conchoidal fracture, non-magnetic and non-radioactive.

[edit] Biographic sketch

Francis Lewis Sperry was a Canadian mineralogist and expert chemist, discovered the mineral sperrylite, which was then named after him. He was a graduate of Sheffield scientific school, Yale University. He was also a member of the American society of mining Engineers. Sperrylite was first described by H. H. Wells (1889) from material collected at the Vermilion mine in what is now the famous Sudbury district, Ontario, Canada. He named it for Mr. Francis L. Sperry, chief chemist with the Canadian Copper Company of Sudbury, who sent him the original material containing the new mineral (Mitchell 1985). It occurred in weathered material with colorless transparent cassiterite [SnO2], which is thought to have been derived from the oxidation of stannite [Cu2(Fe,Zn)SnS4]. Mr. Sperry sent a small quantity of the newly found mineral and also furnished an account of its occurrence in which he said the mineral was found at the Vermillon mine in the district of Algoma, province of Ontario, discovered in October, 1887

[edit] See also

[edit] References

  • Mineral galleries
  • Mindat localities
  • Webmineral
  • Cook, Robert B. (2001) Connoisseur's choice; sperrylite, Talnakh, Noril'sk District, Siberia, Russia. Rocks and Minerals, 0035-7529, Vol. 76, Issue 1
  • Szymański, J.T. (1979) the crystal structure of platarsite, Pt (As, S) 2, and a comparison with sperrylite, PtAs2. Canadian Mineralogist: 17: 117-123.
  • Hidden, W. E. 1898. Occurrence of sperrylite in North Carolina. American Journal of Science 6:381
  • Mitchell, R. S. 1985. Who's who in mineral names: Willard Lincoln Roberts and Francis Lewis Sperry. Rocks & Minerals 60:26-28.
  • Wells, H. H. 1889. Sperrylite, a new mineral. American Journal of Science, vol 37, pp 67-70
  • Seabrooke, C.L. 2004. Platinum-group minerals in the Raglan Ni-Cu-(PGE) sulfide deposit, Cape Smith, Quebec, Canada. Canadian mineralogist. Vol. 42, Part 2, pp.485-497
  • Gait, R. I. 1982. Sperrylite from the type locality. Mineralogical Record 13:159-60
  • Penfield, S. L. 1889. On the Crystalline form of Sperrylite. American Journal of Science. Vol. 37, pp.71-73
  • Goldschmidt, V. 1903. New forms of Sperrylite. American Journal of Science, Vol. 15, pp.450-458