Gold is pretty light for its value. A gram of gold is worth about $50, whereas a US dollar bill (of any denomination) also weighs 1 gram. So gold is 2.5x denser

Gold is pretty light for its value. A gram of gold is worth about $50, whereas a US dollar bill (of any denomination) also weighs 1 gram. So gold is 2.5x denser than $20s. The main flaw with gold as a currency is that it's tempting to shave little bits off each coin so you can melt the shavings into some new coins. Or recast them with 20% lead. Paying in gold coins involved the buyer searching through his pockets for the lightest coins he could foist on the seller, and the seller skeptically hefting and biting them.