Only Gold and Silver were used as money on the silk road.
Explanation:
On silk road, during the medieval period, Silver from the Chinese empires and Gold minted at the Byzantine empire were exclusively used for trade between all participating nations as we know from the coinage of the period.
Any other form of commodity money was not in use as it would have hurt the system of business on the road which was highly organised and regulated by the empires at the both ends of it which were the Byzantines and the Chinese.