Platinum Group metals (Pt, Ir, Pd, Ru, Rh, Os)

Group of precious metals (platinum, iridium, palladium, ruthenium, rhodium, and osmium) that share similar chemical and metallurgical properties.
Most "platinum" used in jewelry is composed of 90% platinum and 10% iridium, which makes it much harder than pure platinum. 5% ruthenium serves same purpose.
Much like gold, platinum purity and alloys are commonly stamped, in abbreviated fashion, on items. Unlike gold, in the U.S., purity is given relative to 1000 parts (per mil), e.g. "950Plat" is 95% pureplatinum.
Palladium and small amount of ruthenium is used in setting heads for platinum jewelry; lighter, less expensive.
Rhodium is used as a plating metal. It gives white gold and platinum a hard, bright finish and slows tarnish on stainless steel.
Platinum has a specific gravity of 21.45.