Gold

The Gold Standard is a system under which nearly all countries fixed the value of their currencies in terms of a specified amount of gold, or linked their currency to that of a country which did so.
As each currency is fixed in terms of gold, exchange rates between participating currencies were also fixed.
Gold is abundant enough to create coins but rare enough so that not everyone can produce them.
Gold doesn't corrode, providing a sustainable store of value, and humans are physically and emotionally drawn to it. Societies and economies have placed value on gold, thus perpetuating its worth.
Gold cannot be destroyed by Water, Time, Fire.
Gold doesn't need Feeding, Fertilizer, Maintenance.
Gold is Malleable, Ductile, Beautiful, Rare.