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September-October 2011

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Connoisseur's Choice: Platinum, Konder Massif, Khabarovsk Territory, Far Eastern Region, Russia

Specimens consisting of the uncombined, or “native,” precious metals are of significant interest to mineralogists, economic geologists, and mineral collectors. Traditionally, these have included gold, silver, and the platinum-group elements. Two of these, gold and silver, have been covered in prior installments of this column (Cook 1994, 2003, respectively). Interestingly, the label gold for any specimen is somewhat generic in that a significantly constrained composition is not implied (as it would be with many minerals), for gold is almost always alloyed with varying amounts of other metals, particularly silver. Platinum is also a generic term with its own set of similar problems. The term platinum can be even more ambiguous and has been used, often incorrectly, to refer to the element itself; the group of elements that includes platinum, palladium, rhodium, iridium, osmium, and ruthenium; the platinum-group of minerals; or the mineral itself, which is almost always an alloy of platinum and iron in a manner analogous to gold and silver in native “gold.” Certain of the platinum-group elements tend to occur together, and alloys of several of them (osmium and iridium, for example) as major components in a single specimen are common and have led to a number of varietal names. When one considers only naturally occurring platinum (the mineral platinum), almost all specimens that contain platinum as the dominant platinum-group metal are alloys of platinum and iron and may or may not contain small amounts of the other platinum-group metals, copper, and gold.

Guest columnist Dr. Robert B. Cook, an executive editor of Rocks & Minerals, is a professor emeritus in the Department of Geology and Geography at Auburn University.

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