cm-3 Melting Point: 2466 C, 4471 F, 2739 K Boiling Point: 4428 C, 8002 F, 4701 K Heat of Fusion: 41.12 kJ.mol-1 Heat of Vaporization: 563 kJ.mol-1 Atomic: Oxidation States: -3, -1, 0, 1, 2, 3, 4, 5, 6 Electronegativity: 2.20 (Pauling scale) Atomic Radius: 136 picometre Covalent Radius: 141 6 picometre Because of its characteristic of being very brittle, pure iridium is quite difficult - almost impossible, in fact - to machine. Estimates place the annual production of rhodium at only about 25 tons. Some of the properties of rhodium are listed below. General: Chemical Symbol: Rh Atomic Number: 45 Category (as an element): Transition Metal Group/ Period/ Block (in the Periodic Table): 9/ 5/ d Atomic Weight: 102.90550 g.mol-1 Electron Configuration: [Kr] 4d8 5s1 Physical: Density (near room temperature): 12.41 g. Similar to the other precious metals in the platinum group, osmium can be found in alloys with copper or nickel. 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. The ranking appears different when the estimated world market prices, per troy ounce, of these nine precious metals are considered (estimates as of January 2010): 1st: Rhodium - USD2,750 2nd: Platinum - USD1,555 3rd: Gold - USD1,131 4th: Palladium - USD424 5th: Iridium - USD408 6th: Osmium - USD380 7th: Rhenium - USD194 8th: Ruthenium - USD173 9th: Silver - USD18 Of the nine precious metals, gold and silver are the best known. As an investment commodity, palladium may be bought in forms of bullion coins or bars. Palladium bullion coins are internationally recognized forms of currency and have the ISO codes XPD and 964. The first known palladium coins to be issued were those of Sierra Leone in 1966. The following year, Tonga started issuing theirs. Silver As An Investment: Ways Of Investing In Silver Silver is like three other precious metals (gold, palladium, and platinum) in terms of being regarded as an investment commodity. In fact, this precious metal has been regarded as a form of currency and a store of value for over four centuries. There are different ways by which one may invest in silver.