Platinum

Properties

Platinum is a grey metal, element 78, symbol Pt, atomic mass 195.08, specific gravity 21.45 (densest of all metals after osmium and iridium),  melting point 1770ºC. There are six stable isotopes, cf. gold (1 stable isotope). It is a refractory noble metal, and relatively non-reactive. It is a truly rare metal: mean abundance in upper continental crust is estimated at just 0.5 ppb, this dearth of the metal a mirror to its presumed, primaeval concentration into the young Earth’s mantle and core.

History

In one early account, platinum was described by Don Antonio Ulloa in a 1748 book, relating details of a trip he made to Colombia in 1735, though it may well have been referred to by Scaliger in 1557. It is possible that gold-platinum alloys were developed by metalsmiths in Ecuador prior to 1000 A.D. The type locality is the Rio Pinto, in the Choco department of Colombia. The name comes from “platina del Pinto”, Spanish for the “little silver” of the Pinto river. It was extensively studied in the late 18th century.

Geology

Platinum is concentrated in specific layers of layered igneous intrusions, the largest of which is the Bushveld complex of South Africa. It is also found in so-called Alaskan-style zoned intrusions, the erosion of which has generated the most productive placer deposits in Russia, Alaska and elsewhere. Platinum and the other PGE are valuable by-products or co-products of nickel and copper in a range of magmatic sulphide ores, and may also be found in chromitites, rocks rich in the chromium-rich oxide chromite, as in the UG-2 Reef of the Bushveld complex.

Mineralogy

Platinum minerals include the native metal (Pt) and platinum-iron alloys in placer deposits, and a range of other compounds found within and proximal to igneous intrusions. Platinum-rich minerals first described in Canada include tulameenite (platinum- iron- copper alloy)  and the more important and very widespread sperrylite, first described by Wells from the Sudbury area in 1889. Sperrylite is a platinum arsenide which is the hard-rock platinum mineral most often large enough to be visible to the naked eye. At the Noril’sk-Talnakh mining district in northwest Siberia, it may rarely attain dimensions greater than 10 mm. PGE minerals are mostly very small, <0.1 mm.

Sources

Platinum was discovered in the Urals of Russia in 1819, near modern Sverdlovsk (Ekaterinburg) and this soon became the major source of the metal, which exceptionally occurs there as kg-scale nuggets. South Africa became the dominant source following the 1924 discovery of the PGE-rich Merensky Reef in the Bushveld complex.  In 2009, major producers were South Africa (76%), Russia (14%) and North America (5%).

Uses

Platinum and other PGE are increasingly seen as an investment, albeit to a lesser extent than gold and silver. Beyond this, all the PGE have important scientific and industrial uses which drive demand. It is used as a catalyst in sulphuric and nitric acid production. Currently, the major uses for platinum are in the jewellery trade and in automotive catalysts to reduce the flux of polluting exhaust gases. Traditional uses in coinage, dental equipment, laboratory crucibles, resistance thermometers and thermocouples, and glass production are augmented by anti-cancer drugs like cisplatin, and special hearing aids.