Credit vs bullion
Gold can be distinguished from credit by one essential feature. It can be stolen. More seriously, it requires less trust and less commitment. Hard currency predominates in uncertain times.
Graeber describes long cycles which alternate between virtual and metal money.
3500-800 bc. Credit. Early agrarian empires.
800 bc-600 ad. Metal. Axial age, the rise of coinage.
600-1450 ad. Credit. Middle ages.
1450-1971. Metal. Capitalist empires.