Platinum-Group Minerals

Abstract

The six elements platinum (Pt), palladium (Pd), osmium (Os), iridium (Ir), ruthenium (Ru) and rhodium (Rh) are collectively known as the platinum-group elements (PGE). They share some common geochemical characteristics and, in consequence, they often occur together in rocks and minerals. These elements provide the principle constituents of platinum-group minerals (PGM). To form PGM, the PGE can combine with each other, with elements such as iron, sulfur, arsenic, antimony, tellurium, bismuth, tin or lead. Rarely, they occur as minerals of the native elements. Together this allows the existence of a very large number of possible combinations. Some 147 PGM have currently been sufficiently characterized to be accepted by the International Mineralogical Association Commission on New Minerals and Mineral Names (IMA CNMMN) as viable mineral species. There are many more examples, some also known as synthetic phases, which have been observed as minute occurrences within rocks but they are currently not fully characterized by knowledge of their structure, chemistry and other properties. Future study is likely to lead many of them joining the list of recognized PGM presented here. The PGM are most usually associated with basic and ultrabasic rocks such as layered gabbros, dunites, chromitites and ophiolites. Initially formed by magmatic processes they can be subject to metamorphic, hydrothermal and secondary alteration and re-crystallization.