Tetraferroplatinum
Chemical formula: PtFe
Tetragonal natural alloy of platinum and iron, occurring as metallic grains in ultramafic rocks.
Description
## Characteristics Tetraferroplatinum is a platinum group mineral, a natural alloy of platinum and iron. It forms metallic, opaque grains and nuggets, ranging in color from steel-gray to black. Small, imperfectly formed crystals with a distorted cubic or octahedral appearance are rarely observed. It usually occurs as irregular inclusions in other minerals, especially chromite. ## Physical Properties This mineral is characterized by a strong metallic luster and is opaque. Its Mohs hardness is 4 to 5, which means it is harder than pure platinum. It is a very dense mineral, with a density calculated from the formula and cell parameters of approximately 15.1 g/cm³. It is malleable and ductile. ## Colors and Varieties The color of tetraferroplatinum is uniform and ranges from steel-gray to black, depending on the surface condition. It does not form color varieties or commercial varieties. ## History and Name The mineral was formally described and named in 1975 by Louis J. Cabri and C. E. Feather. The name "tetraferroplatinum" refers to its tetragonal crystallographic system ("tetra") and its chemical composition – iron ("ferro") and platinum. ## Applications Tetraferroplatinum, as a component of platinum ores, is exploited along with other platinum-bearing minerals. It is primarily of scientific and collectible importance, being of interest to specialized collectors of platinum group minerals.
Diagnostic features
## Identification A key diagnostic feature is its very high density, which can be felt even in small specimens. Other features include metallic luster, steel-gray or black color, black streak, and malleability. Its occurrence in association with chromite and other ultramafic rock minerals is a strong indicator. ## Distinguishing from Similar Minerals Identifying tetraferroplatinum and distinguishing it from other platinum group minerals (PGMs) with a similar appearance (e.g., cubic isoferroplatinum) is impossible without advanced analytical methods such as X-ray diffraction (XRD) or microprobe analysis (EDS/WDS). It is distinguished from magnetite by its lack of magnetism, and from chromite by its lower hardness and black streak (chromite's streak is brown). ## Crystal Forms Crystals are very rare and usually small (below 1 mm), taking the form of distorted cubes and octahedra. It is most commonly found as irregular grains, nuggets, placers, or inclusions in other minerals.
Geological environment
## Genesis Tetraferroplatinum is a magmatic mineral, crystallizing at high temperatures within ultramafic and mafic rocks, such as dunites, peridotites, and pyroxenites. It is particularly characteristic of layered intrusions, where it concentrates in chromite-rich horizons (chromitites). ## Mineral Associations This mineral co-occurs with other platinum group minerals (PGMs), such as isoferroplatinum, braggite, cooperite, as well as with chromite, magnetite, olivine group minerals, and pyroxene. ## Localities Key global localities include deposits in the Bushveld Complex in South Africa (e.g., in the Mooihoek and Onverwacht areas, which are type localities), in the Ural ultramafic massifs in Russia (Nizhny Tagil area), in the Tulameen Complex in British Columbia (Canada), and in Freetown, Sierra Leone.
Rarity
Rare
Collector aspects
## Quality Criteria The most valuable specimens for collectors are those with visible, even if imperfectly formed, crystals. Rich accumulations of tetraferroplatinum grains on a rock matrix or in polished ore samples (polished sections) are also highly prized. The size of grains and nuggets is a significant factor influencing value. Origin from a classic, historical locality, such as the Urals, also increases the attractiveness of the specimen. ## Popular Localities Specimens from the historical deposits in the Urals in Russia and from the Bushveld Complex in South Africa are considered classic and most desired by collectors specializing in platinum group minerals.
Care and storage
## Cleaning Tetraferroplatinum specimens are stable and do not require complex care. A soft brush is sufficient to remove dust and minor impurities. If necessary, distilled water can be used. Ultrasonic cleaning is generally safe, but caution should be exercised with specimens on a delicate matrix. ## What to Avoid The mineral is relatively soft, so it should be protected from contact with harder minerals that could scratch it. Despite its high chemical resistance, contact with strong acids should be avoided. Falls and impacts that could damage the specimen should also be avoided. ## Storage It is recommended to store specimens in separate, padded boxes or display cases to prevent scratching. A label with the location and mineral name should be permanently assigned to the specimen.