Commodity money cans or foil pouches of mackerel fish fillets, which have a fairly standard cost and are easy to store. These may be exchanged for many services in prisons where personal possession of currency is prohibited. In situations where the commodity is metal, typically gold or silver, a government mint will often coin money by placing a mark on the metal that serves as a guarantee of the weight and purity of the metal. In doing so, the government will often impose a fee which is known as seigniorage. The role of a mint and of coin differs between commodity money
Commodity (Marxism) of socially necessary labor have the same exchange value. By contrast, prices are normally measured in money-units. For practical purposes, prices are, however, usually preferable to labour-hours, as units of account, although in capitalist work processes the two are related to each other (see labor power). The seven basic forms of commodity trade can be summarised as follows: The hyphens ("-") here refer to a transaction applying to an exchange involving goods or money; the dots in the last-mentioned circuit ("...") indicate that a value-forming process ("P") occurs "in between" purchase of commodities and the sales of different commodities. Thus,