Sperrylite

Sperrylite is platinum arsenide (PtAs2), the most important and widespread platinum mineral and the principal mineralogical source of mined platinum. It crystallizes in the cubic system, forming bright tin-white to silver-gray metallic crystals, often as small cubes, octahedra, and combinations.

Discovered near Sudbury, Ontario, it was named after the chemist Francis Sperry. Despite its economic importance, well-formed crystals are rare and prized.

Sperrylite is hard for a metallic mineral and unusually durable, and its bright luster and crystal form make fine specimens striking museum and collector pieces.

Sperrylite forms in magmatic nickel-copper sulfide deposits associated with mafic and ultramafic igneous rocks, where platinum-group elements concentrate during the crystallization and segregation of sulfide melts.

It typically occurs as tiny grains and occasional crystals disseminated within or alongside pyrrhotite, pentlandite, and chalcopyrite in these ore bodies.

The classic localities are the Sudbury Basin in Ontario, Canada, and the Bushveld Complex in South Africa, the world's greatest platinum-group element province. It is also found in the Norilsk deposits of Russia and in some placer concentrates.

Sperrylite is identified by its bright tin-white to silver-gray metallic luster, cubic and octahedral crystal forms, and notable hardness of 6 to 7, which is high for a metallic mineral and a useful diagnostic.

Its streak is black, and it is dense due to its platinum content. The combination of bright metallic cubes with high hardness helps distinguish it from softer metallic sulfides and arsenides like pyrite (which is also hard but pale brassy) and cobaltite.

Because crystals are usually tiny and embedded in sulfide ore, context within a platinum-bearing deposit is an important clue.

Sperrylite is the single most important ore mineral of platinum, which is essential for catalytic converters, chemical and petroleum catalysts, electronics, laboratory equipment, and jewelry.

The great nickel-copper-platinum mines of Sudbury and the Bushveld Complex recover platinum largely as sperrylite from sulfide ores, giving the mineral major economic significance.

For collectors, sharp metallic sperrylite crystals are rare and highly valued, with fine examples being scarce museum-grade specimens. It contains arsenic, so specimens should be handled sensibly, though their hardness limits dust formation.