Along with the five other precious metals in the platinum group, ruthenium is generally found in ores in North America, South America, and the Ural Mountains in Russia. Small quantities of this element also occur in pentlandite (an iron-nickel sulfide) obtained from Sudbury in Ontario, Canada, and in South Africa's pyroxenite (an ultrabasic igneous rock) deposits. Three Methods Of Assay For Raw Precious Metals Items of jewelry or art made of precious metals are hallmarked based on specific requirements either of the country of import or the place of manufacture. Such items, particularly those made of silver, gold, or platinum, are struck with an official mark (or series of marks), which guarantees fineness or purity of the metal used. Rhodium: Although rhodium is inert (being a noble metal, as almost all the other precious metals are), it can be reactive, especially if used as compounds. In its basic form, however, rhodium is not known to cause any harm. Iridium: Iridium, when finely divided, can pose some hazards - it can ignite in air. The extreme toxicity and volatility of osmium's oxide makes it nearly impossible for this element to be used in its pure state. For this reason, it is often necessary to alloy osmium with other elements for use in high-wear applications. For example, osmiridium (a natural alloy of osmium and iridium) is alloyed with the other metals in the platinum group and used in instrument pivots and phonograph needles (apart from electrical contacts and fountain pen tips as mentioned earlier). These are Australia, Austria, Canada, China, Mexico, Poland, South Africa, Switzerland, the United Kingdom, and the United States. While bullion coins are issued as legal tender, with nominal values assigned to them on minting, such face values are far below the commodity value of the metals themselves. mol-1 Heat of Vaporization: 250.58 kJ.mol-1 Atomic: Oxidation States: 1, 2, 3 Electronegativity: 1.93 (Pauling scale) Atomic Radius: 144 picometre Covalent Radius: 145 5 picometre Van der Waals Radius: 172 picometre Ionization Energies: 731 kJ.mol-1 (first), 2070 kJ.mol-1 (second), 3361 kJ.mol-1 (third) Despite having higher electrical conductivity than copper, silver isn't as much used for electrical purposes as copper is.