Gold rules the world. ~ German proverb
Gold has long held a special place in the materialism of man. Its reddish-yellow color and soft luster have an undeniable appeal. But that is only gold’s initial allure.
As a storehouse of value, gold’s unique property is its ability to resist what used to be known as decay but is now called chemical attack. Besides its relative scarcity, gold became precious because it was incorruptible. No acid or alkali known to ancients could diminish it.
Gold is readily processed, and its quality easily assayed. Gold has a low melting point: 1000º C, almost the same as copper. Using a hoary process called cupellation, pure gold may be separated from whatever dross it is with.
Quality assessment is even simpler. By treating a claimed gold object with an acid, its purity may be ascertained. If it does not decay, it is pure gold.
Silver has been the other precious metal used as a monetary unit. Silver is much more abundant and not nearly as incorruptible. Significant silver finds at various times in history caused price fluctuations that made it less desirable than gold as a currency unit. As a backing for currency, stability is prized above all else.
Gold is rare on Earth because it is scarce throughout the cosmos. Unlike elements like carbon, or iron, which is the densest production by stars before going supernova, gold can only be made via the collisions of neutron stars, which are the densest stellar remnants.