Gem materials

A gem material is a naturally occurring substance valued as ornament for the combination of three properties: rarity, durability enough to survive cutting and wear, and beauty of color, luster, or transparency. None of the three suffices alone, which is why common minerals of great beauty and beautiful minerals too soft to wear are both excluded. The category holds transparent stones — tanzanite, beryl as emerald and aquamarine, spinel, tourmaline, peridot, garnet, topaz, amethyst — opaque and translucent ones such as lapis lazuli, jade, opal, turquoise, and malachite, and the organic gems, pearl and coral.

One structural fact separates this category from everything else on the list: gems are not fungible. Every other commodity here trades by weight or volume against a specification, and that interchangeability is what makes an exchange, a benchmark price, and a forward contract possible — a ton of refined copper is a ton of refined copper wherever it sits. A gemstone is priced as an individual object, and two stones of the same species and identical weight can differ in value by orders of magnitude on color, clarity, and cut. So this category has no exchange, no benchmark, and no futures market, and its trade runs instead on the expert appraisal of single objects, which is also why it has always been unusually hospitable to fraud. The separate category for diamonds is the exception that demonstrates the rule, because the real achievement of the diamond cartel was to manufacture fungibility where none existed, by grading, sorting into defined categories, and selling in fixed parcels at set prices.

The commodity is the stone at every stage from rough crystal to finished gem, since cutting does not change what it is — the same relation that dimension stone bears to the quarry. Treatment should not be assumed away: most tanzanite on the market is heat-treated zoisite, and heating, irradiation, oiling, and dyeing are routine across the category rather than exceptional. Synthetic stones of identical composition belong here too, because a lab-grown emerald is an emerald; what separates it from a mined one is disclosure and price, not substance. A finished piece of jewelry is a manufactured good, and its setting is gold, silver, or platinum.

Pearl supplies this category's great substitution, and it is the best-documented of them. Gulf pearling ran for four millennia and at its height was the principal economy of the Arabian coast: Lorimer counted 917 boats at Bahrain in 1905, with 410 at Abu Dhabi, 350 at Doha, and 335 at Dubai, and a Bahrain workforce above 17,500 men. Bahrain's pearl exports were valued at #1,076,793 in 1904/05, and some nine million dollars' worth were sold from Bahrain in the 1913 season alone. The trade ran on credit, merchants advancing money to boat captains who fed and clothed their crews on it, and the divers and haulers at the bottom were frequently people who had been enslaved in Africa and South Asia — so an entry on Gulf pearling would carry slaves alongside this category. Mikimoto's cultured-pearl industry began in Japan in 1916 and sold at up to a tenth of the Gulf price. The fleets shrank through the 1920s, Bahrain's population fell from about 100,000 in 1908 to 90,000 by 1941 and Doha's from 27,000 to 16,000 across the 1930s, and by the early 1950s, with oil arriving, pearling had all but disappeared. A wild commodity was ended by a cultivated one, two decades before nylon did the same to silk.

The exclusions are settled: diamonds, corundum, ivory, and amber have categories of their own. Beyond those, the oyster and the coral polyp are fish and game while the pearl and the worked coral are here. Lapis lazuli as a stone is here; ground to ultramarine it is a colorant, and malachite and azurite divide the same way. Obsidian keeps its own category even when worked as ornament. A stone valued by the ton for building or facing is rocks, sand, and gravel, and the same stone valued by the carat is here. The category's date is c. 4000 BCE, on lapis lazuli carried from Badakhshan to Mesopotamia — some two thousand kilometers from a single Afghan valley, and the earliest evidence on this list of a long-distance trade conducted purely for ornament.