Often they are concentrated by watercourses and recovered by placer mining. In other instances, gold nuggets are found in piles of residue in sites where mining operations once took place. Two gold nuggets are noted for being the largest masses of gold ever discovered. These are the "Welcome Stranger" and the "Hand of Faith". Gold bars however are becoming less and less an option among investors due to the difficulties (in the verification process, transportation, and storage) associated with them. Opening a gold account: Gold accounts are offered by most banks in Switzerland. Here, gold can be bought or sold in much the same way foreign currencies are dealt. mol-1 (third) The principal use of rhodium is as a catalytic converter in automotive vehicles, which reduces the toxicity of engine emissions by converting these into less harmful gases. Rhodium is likewise used in jewelry, such as when it is electroplated on platinum, sterling silver, or white gold (called rhodium flashing) to strengthen the metal or give it a reflective surface. The estimated total resource from these eight countries is 6,000 tonnes (6 million kilograms). The United States alone, on the other hand, has an estimated total resource of 5,000 tonnes (5 million kilograms). These are identified in the states of Arizona, Miami, and Utah. But in spite of these significant resources, the U. 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. In fact, this is shown even in temperatures of as high as 2000 C (3632 F or 2273.15 K). Iridium was discovered in 1803 by the English chemist Smithson Tennant. It was identified from the residue of platinum ore which was dissolved in nitro-hydrochloric acid (also known as aqua regia). Platinum ores are still the main sources today of iridium.