The native platinum group elements (PGE), namely, the light PGE (ruthenium, rhodium and palladium) and the heavy PGE (osmium, iridium and platinum), are important historically, scientifically and industrially. Some of the scientists who discovered and refined these metals in the 18th and early 19th centuries, besides being chemists, were also physicians, but all were also knowledgeable of mineralogy. We cannot but be impressed by their achievements because of the complexity of the minerals they studied. The PGE alloys occurred as a fraction of the heavy minerals concentrated from alluvial deposits. Today we can understand why some details of their discovery and mineralogy have not been well understood because of a lack of modern mineralogical studies and misunderstandings of some of the early literature, especially for native palladium and platinum. Though reported widely, highlights of the historical discoveries are here assembled in a single paper and discussed with respect to the mineralogy of the samples studied.
New dilatometric measurements allow the evaluated thermal expansion of osmium to be increased from the previous limit of 1300 K to the melting point at 3400 K. The new data is reported in the form of Equations and Tables. The revision confirms that osmium is the densest solid at all temperatures above room temperature. A new equation is given for the density of liquid osmium.
