Other countries later began issuing their own palladium bullion coins, including Canada (with its Big & Little Bear Constellations and the very popular Palladium Maple Leaf), Australia, France, China, Portugal, and the former Soviet Union. The latter, in fact, is known to have minted the most number of palladium coins in the world. Being rare and, therefore, very precious, platinum has been made synonymous to things that are considered "of the highest quality". We hear for instance of a platinum debit card holder enjoying a wide range of privileges; or of a platinum award being handed out to a music album that has sold over a million copies. Apart from this, accidental exposure to a radioisotope of iridium may cause poisoning by radiation, burns, and even death. Ruthenium: Three conditions may be associated with exposure to ruthenium: it can stain the skin; it may accumulate in bones; and it may increase the risk of cancer. Ruthenium tetroxide, a yellow, diamagnetic tetrahedral ruthenium compound, is highly toxic and volatile; it may explode if it comes into contact with combustible materials. By strict definition, precious metals are those metallic elements that are rare. Bullion is commonly made of either gold or silver. Its value is determined by the worth of the metal rather than by its face value as money. To put it another way, bullion is valued based on the mass and purity of the metal used, instead of its artificial currency value. In this method, mined ore is placed in a large pan (made either of plastic or metal) and poured with a liberal amount of water; it is then agitated. The gold particles, having higher density than the other materials (examples, mud, sand and gravel; also, gold is about nineteen times heavier than water), settle to the bottom of the pan, while the lighter materials are washed over the side. ) coin - With a face value of USD10, 3.112 grams (g) in weight, 0.95 millimeters (mm) thick, and 16.5 mm in diameter. 2. 1/4 oz. coin - With a face value of USD25, 7.78 g in weight, 1.32 mm thick, and 22 mm in diameter. 3. 1/2 oz. coin - With a face value of USD50, 15.56 g in weight, 1.75 mm thick, and 27 mm in diameter.