According to [1] which references [2]: An element must meet four qualities to stand alone as a premium currency... First, it can't be a gas — gases simply are

According to [1] which references [2]: An element must meet four qualities to stand alone as a premium currency... First, it can't be a gas — gases simply are not practical for currency exchange... Second, it can't be corrosive or reactive... Third, it can't be radioactive. [Fourth, it] must be rare enough to be valuable, but not so rare that it's impossible to find. That brings us to five elements: rhodium, palladium, platinum, silver and gold. Although silver has been used for currency, it tarnishes easily, so it's out. Rhodium and palladium were discovered only in the 1800s, so they'd have been of no use to early civilizations. That leaves gold and platinum. Platinum, however, has a melting point around 3,000 degrees Fahrenheit (about 1,600 degrees Celsius), which could only be attained in a modern furnace, so early civilizations would not have been able to conveniently shape it into uniform units. [1] https://www.livescience.com/32863-gold-best-element-money.html https://www.livescience.com/32863-gold-best-element-money.ht... [2] https://www.npr.org/sections/money/2011/02/15/131430755/a-chemist-explains-why-gold-beat-out-lithium-osmium-einsteinium https://www.npr.org/sections/money/2011/02/15/131430755/a-ch...