A real currency must be based on a commodity. Fiat, or
paper money, is simply an IOU, with no collateral, but a commodity
currency, uses the commodity as collateral.
In the latter currency, the commodity to be used must be
a universally accepted collateral, capable of being stored in Central
Banks, be of a singular grade, and be denominational.
Items like cattle, chickens, lumber, real estate, oil,
etc, come in different grades, aren't static, and wouldn't store at
Fort Knox. The only workable commodities are the precious metals like
gold and silver.