大唐西域記 2.18: 18. Commercial Transactions.

2.18

Gold and silver, teou-shih (native copper), white jade, fire pearls, are the natural products of the country; there are besides these abundance of rare gems and various kinds of precious stones of different names, which are collected from the islands of the sea. These they exchange for goods; and in fact they always barter in their commercial transactions, for they have no gold or silver coins, pearl shells, or little pearls.
The boundaries of India and the neighbouring countries are herein fully described; the differences of climate and soil are briefly alluded to. Details referring to these points are grouped together, and are stated succinctly; and in referring to the different countries, the various customs and modes of administration are fully detailed.