Yellow metallic element, with an atomic weight of 197.2 and a specific gravity of 19.32. It is one of the so-called ‘noble’ metal group, which also includes silver and platinum. Gold has always been highly valued for its intrinsic beauty, its working properties, and its rarity—until recent times it was used to underpin the currencies of the major trading nations, and it is still a traditional refuge in times of financial instability. It is first known to have been worked in Mesopotamia in the 6th millennium BC. Since then it has been prized as a material to fashion or to decorate a wide variety of objects, including jewellery, coins, ritual items, tableware, and furniture. A scarce element, representing between 1 and 9 mg per tonne in the composition of the earth, gold is found mainly in the native state, in contrast with most other metals, which are found as ores. Deposits of gold occur either in the original formations (e.g. as veins in quartz) or as ‘placer’ in alluvial deposits.