Pound (mass) a legal unit for trade (it was abolished in the United Kingdom on 6 January 1879 by the Weights and Measures Act of 1878), but the troy ounce, of a troy pound, is still used for measurements of gems such as opals, and precious metals such as silver, platinum and particularly gold. The system called Tower weight was the more general name for King Offa's pound. This dates to 757 AD and was based on the silver penny. This in turn was struck over Arabic dirhams (2d). The pound was based on the weight of 120 Arabic silver dirhams, which
Precious metal coinage. Other precious metals include the platinum group metals: ruthenium, rhodium, palladium, osmium, iridium, and platinum, of which platinum is the most widely traded. The demand for precious metals is driven not only by their practical use but also by their role as investments and a store of value. Historically, precious metals have commanded much higher prices than common industrial metals. A metal is deemed to be "precious" if it is rare. The discovery of new sources of ore or improvements in mining or refining processes may cause the value of a precious metal to diminish. The status of a