3 ideas
Pliny calculates that India, China and Arabia draw at least 100 million sesterces a year out of the empire, and he blames this on Roman demand for pearls, silks, spices and perfumes. His point is that consumer taste for useless luxuries is a real economic cost. The empire's coinage flows east and does not come back, all to pay for vanity.
Pliny catalogues each substance by where it comes from, how it is adulterated, how to test whether it is genuine, what it is used for, and what it sells for per pound. Looked at this way, nature becomes a market ledger. Value is set by scarcity, fraud and fashion rather than by intrinsic properties, and the price itself becomes evidence about a society's desires.
Pliny reports that he drew about 20,000 facts from some 2,000 volumes by 100 authors. He names his sources for each book and opens the whole work with a table of contents so readers can go straight to a topic instead of reading straight through.