Sperrylite is a

platinum Platinum is a chemical element with the symbol Pt and atomic number 78. It is a dense, malleable, ductile, highly unreactive, precious, silverish-white transition metal. Its name originates from Spanish , a diminutive of "silver". Pla ...

arsenide In chemistry, an arsenide is a compound of arsenic with a less electronegative element or elements. Many metals form binary compounds containing arsenic, and these are called arsenides. They exist with many stoichiometries, and in this respect a ...

mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid chemical compound with a fairly well-defined chemical composition and a specific crystal structure that occurs naturally in pure form.John P. Rafferty, ed. (2 ...

with the chemical formula and is an opaque metallic tin white mineral which crystallizes in the isometric system with the

pyrite group The pyrite group of minerals is a set of cubic crystal system minerals with diploidal structure. Each metallic element is bonded to six "dumbbell" pairs of non-metallic elements and each "dumbbell" pair is bonded to six metal atoms. The group is n ...

structure. It forms cubic, octahedral or pyritohedral

crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, forming a crystal lattice that extends in all directions. In addition, macro ...

s in addition to massive and reniform habits. It has a

Mohs hardness The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by t ...

of 6 - 7 and a very high

specific gravity Relative density, or specific gravity, is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for liquids is nearly always measured with respect to water at its densest ...

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 Nickel is a chemical element with symbol Ni and atomic number 28. It is a silvery-white lustrous metal with a slight golden tinge. Nickel is a hard and ductile transition metal. Pure nickel is chemically reactive but large pieces are slow ...

ore Ore is natural rock or sediment that contains one or more valuable minerals, typically containing metals, that can be mined, treated and sold at a profit.Encyclopædia Britannica. "Ore". Encyclopædia Britannica Online. Retrieved 7 Apr ...

deposit of Sudbury Basin in

Ontario Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central C ...

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

. It also occurs in the layered

igneous Igneous rock (derived from the Latin word ''ignis'' meaning fire), or magmatic rock, is one of the three main rock types, the others being sedimentary and metamorphic. Igneous rock is formed through the cooling and solidification of magma or ...

complex of the

Bushveld The Bushveld (from af, bosveld, af, bos 'bush' and af, veld) is a tropical and subtropical grasslands, savannas, and shrublands, sub-tropical woodland ecoregion of Southern Africa. It encompasses most of Limpopo Province and a small part of ...

region of

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. It is bounded to the south by of coastline that stretch along the Atlantic Ocean, South Atlantic and Indian Oceans; to the ...

and the Oktyabr'skoye copper-nickel deposit of the Eastern-Siberian Region,

Russia Russia (, , ), or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world, with its internationally recognised territory covering , and encompassing one-eig ...

Geologic occurrence

Sperrylite is the most common platinum mineral, it generally occurs with a wide array of other unusual minerals, including cooperite [], laurite [], kotulskite [], merenskyite [], iridium-osmium (Ir-Os) alloys, sudburyite [], omeiite [], testibiopalladite [], and niggliite [], to name a few. It does not readily decompose through normal

weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement) ...

processes and, consequently, has been reported in widely scattered

alluvial deposits Alluvium (from Latin ''alluvius'', from ''alluere'' 'to wash against') is loose clay, silt, sand, or gravel that has been deposited by running water in a stream bed, on a floodplain, in an alluvial fan or beach, or in similar settings. Alluv ...

. It was first found as tiny crystals found with

rhodolite Rhodolite is a varietal name for rose-pink to red mineral pyrope, a species in the garnet group. It was first described from Cowee Valley, Macon County, North Carolina. The name is derived from the Greek "rhodon" for "rose-like", in common wi ...

garnet Garnets () are a group of silicate minerals that have been used since the Bronze Age as gemstones and abrasives. All species of garnets possess similar physical properties and crystal forms, but differ in chemical composition. The different s ...

and corundum during alluvial gem mining in streams draining Mason Mountain,

Macon County, North Carolina Macon County is a county located in the U.S. state of North Carolina. As of the 2020 census, the population was 37,014. Its county seat is Franklin. The Nantahala River runs through Macon County, flowing into the Little Tennessee River in S ...

(Hidden 1898). Sperrylite has been identified in

Finland Finland ( fi, Suomi ; sv, Finland ), officially the Republic of Finland (; ), is a Nordic country in Northern Europe. It shares land borders with Sweden to the northwest, Norway to the north, and Russia to the east, with the Gulf of B ...

from sulfide deposits generally associated with layered mafic-ultramafic complexes.

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 (ideally PtAsS). 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 Metamorphism is the transformation of existing rock (the protolith) to rock with a different mineral composition or texture. Metamorphism takes place at temperatures in excess of , and often also at elevated pressure or in the presence of che ...

, as in indicated by the development of

triple point In thermodynamics, the triple point of a substance is the temperature and pressure at which the three phases (gas, liquid, and solid) of that substance coexist in thermodynamic equilibrium.. It is that temperature and pressure at which the sub ...

annealing contacts with

pyrrhotite Pyrrhotite is an iron sulfide mineral with the formula Fe(1-x)S (x = 0 to 0.2). It is a nonstoichiometric variant of FeS, the mineral known as troilite. Pyrrhotite is also called magnetic pyrite, because the color is similar to pyrite and it i ...

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.

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 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 crystal system, Conchoidal fracture, non-magnetic and non-radioactive.

Discovery

Sperrylite was first described by H. H. Wells in 1889 from material collected at the Vermilion mine in what is now the

Sudbury district The Sudbury District is a district in Northeastern Ontario in the Canadian province of Ontario. It was created in 1894 from townships of eastern Algoma District and west Nipissing District. The overwhelming majority of the district (about 92%) ...

Ontario, Canada Ontario ( ; ) is one of the thirteen provinces and territories of Canada.Ontario is located in the geographic eastern half of Canada, but it has historically and politically been considered to be part of Central Canada. Located in Central C ...

. He named it for Francis L. Sperry, chief chemist with the Canadian Copper Company of Sudbury, who collected the original material in 1887 (Mitchell 1985). It occurred in weathered material with colorless transparent cassiterite [], which is thought to have been derived from the oxidation of stannite [].

References

*Cook, Robert B. (2001) Connoisseur's choice; sperrylite, Talnakh, Noril'sk District, Siberia, Russia. Rocks and Minerals, , 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 {{ores Platinum minerals Arsenide minerals Pyrite group Cubic minerals Minerals in space group 205 Minerals described in 1889

Geologic occurrence

Structure

Physical properties

Discovery

See also

References