The discoveries of iridium (named after Iris, goddess of the rainbow, because of the variegated colour of its salts) and osmium (from the Greek word for "odour," because of the chlorinelike odour of its volatile oxide) were claimed by the English chemist Smithson Tennant in 1803.
Fire assay is considered the most reliable method for accurately determining the content of gold, silver, and platinum-group metals (except osmium and ruthenium) in ores or concentrates.
Noble metal, any of several metallic chemical elements that have outstanding resistance to oxidation, even at high temperatures; the grouping is not strictly defined but usually is considered to include rhenium, ruthenium, rhodium, palladium, silver, osmium, iridium, platinum, and gold; i.e., the metals of groups VIIb, VIII, and Ib of the second and third transition series of the periodic table.
The most common native metals, which are characterized by simple crystal structures, make up three groups: the gold group, consisting of gold, silver, copper, and lead; the platinum group, composed of platinum, palladium, iridium, and osmium; and the iron group, containing iron and nickel-iron.
Elemental ruthenium occurs in native alloys of iridium and osmium, along with the other platinum metals: up to 14.1 percent in iridosmine and 18.3 percent in siserskite.
Although the osmium he used was too rare for general use, his improvement paved the way for the tungsten filament and the modern light bulb.
The residue left over from leaching the original mineral concentrate contains rhodium, iridium, ruthenium, and osmium.
These native elements are commonly divided into three groups namely, metals (platinum, iridium, osmium, iron, zinc, tin, gold, silver, copper, mercury, lead, chromium); semimetals (bismuth, antimony, arsenic, tellurium, selenium); and nonmetals (sulfur, carbon).
Tennant undertook the analysis of the less-soluble constituents of the platinum ore and discovered two other new metals, osmium and iridium.
The rhenium osmium ratio in most minerals is too low to be of general use as a dating technique, but molybdenite (molybdenum disulfide, MoS2) has a very high ratio of rhenium to osmium; and workers have found that the osmium in molybdenite is practically pure radiogenic osmium-187.
Platinum group, six metals, in order of increasing atomic weight, ruthenium (Ru), rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir), and platinum (Pt).
