Gold is highly malleable, that is it can be rolled into very thin gold leaf. Gold doesn't oxidize at ordinary temperatures, so no oxide film dulls its surface. It is an excellent conductor of electricity hence is used extensively in microchips. The high reflective properties of gold make it useful for heat protection on solar vehicles and for applications in the space program. It's rarity and inertness makes gold an obvious choice as the medium for coinage.
Fineness describes the purity of gold.
Secondary gold usually has a higher purity than primary gold.