The platinum-group elements (PGE) tend to exist in the metallic state or bond with sulfur or other Group Va and VIa ligands, and often occur as trace accessory minerals in rocks. Combined with three isotopic systems that contain the PGE, these elements afford a unique view of early solar system evolution, planet formation and differentiation, and biogeochemical cycling. Initial purification of the PGE was accomplished in the late 1700s, at which time their unique properties, including high melting point, chemical inertness, and ability to catalyze chemical reactions, became apparent. This led to enormous industrial demand, most notably for fuel production and engine emission control, which combined with scarcity in crustal rocks, has made the PGE a highly valued commodity.

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