Wollaston's and Tennant's discovery of the element involved the discovery as well of the other elements in the platinum group. With an average mass fraction of 0.05 parts-per notation in the continental crust, osmium is known to be one of the least abundant elements in the Earth's crust. It is found in nature in natural alloys or as a pure element. Its principal use is for electrical purposes, mainly because of its density and its high resistance to corrosion even at extremely high temperatures. Iridium is considered the fourth least abundant element in the Earth's crust, after rhenium, ruthenium, and rhodium. Its price is estimated to be about USD408 per troy ounce (USD13,117 per kilogram) as of January 2010. But while platinum is generally resistant to corrosion, it is corroded by certain elements, such as cyanides (potassium cyanide or sodium cyanide), caustic alkalis, sulfur, and any of the five halogens (astatine, bromine, chlorine, fluorine, and iodine). The following lists some of the properties of platinum: General: * Chemical Symbol: Pt * Atomic Number: 78 * Category (as an element): Transition Metal * Group/ Period/ Block (in the Periodic Table): 10/ 6/ d * Atomic Weight: 195.084 g. It can be plated by means of two methods: thermal decomposition and electrodeposition. Following is a list of some of the properties of ruthenium: General: Chemical Symbol: Ru Atomic Number: 44 Category (as an element): Transition Metal Group/ Period/ Block (in the Periodic Table): 8/ 5/ d Atomic Weight: 101.07 g. Again, the X-ray fluorescence (XRF) method is the modern assay method widely used today for analyzing precious metals, including (besides silver, gold, and platinum) rhenium, ruthenium, iridium, and palladium. As a non-destructive assay method, XRF can identify various elements in a substance (in fact, even in powder and liquid ones) within a few minutes. continues to import a big part of its total consumption of the precious metal from some of the countries mentioned above. Since rhenium and its compounds are used in very small amounts, very little is known about their toxicity. So far, only a few rhenium compounds have been tested for toxicity, and these include rhenium trichloride and potassium perrhenate.