A form of money that has gone out of use is "commodity money". This type of money was based on the value of a commodity, such as gold, silver, or salt, and was widely used in the past. The actual commodity was used as currency and had value in and of itself. For example, gold coins were used as a form of payment and the value of the coins was determined by the amount of gold they contained. However, as economies evolved and grew, commodity money became impractical due to issues such as security and portability. As a result, paper money and bank money, which are more convenient and easier to use, gradually replaced commodity money as the primary forms of currency.