The most popular gemstone in the world today is the diamond. We expect fine jewelry to have few colors, or possibly even none at all. The most expensive tiaras are so encrusted with diamonds that they appear to be pure white. This, however, was not medieval Europe’s idea of fine jewelry.
Through most of the Middle Ages, of course, the Islamic empire in one form or another controlled and guarded trade with the East. Imported gemstones mostly came from or through their territories, often by ship between India and the Arabian and Egyptian ports. Egypt itself had a large deposit of emeralds. Rubies came from India, sapphires from Ceylon and Persia. Persia also sent turquoise and lapis lazuli; some turquoise came from Tibet, one of the more distant points on the Silk Road. Most garnet came from Russia, probably traded through Constantinople.
Diamonds had to be imported from India and Africa, but that alone would be a point in their favor, since scarcity and cost were as important then as now. But until the late Middle Ages, gems were mounted uncut. If you look at the Oppenheimer Diamond, which is displayed in the Smithsonian, you can see why uncut diamonds did not catch on. It’s white and yellow, but it doesn’t refract light the way we’ve come to expect by seeing only cut diamonds. The other imported gems had vibrant colors that served as decoration even in round, polished form. Only diamonds have no real decorative value until they’re cut.
The first diamond cutters’ guild was established in 1375, in Nuremberg, Germany. Because Germany had such rich minerals in its mountains, it became the leader in all things having to do with metals, minerals and early chemistry. Diamonds’ greatest value may have been as cutting tools, more than as jewels. In fact, that may be where the tradition of diamond rings came from: a ring with a cut diamond could be used to write on glass.
Pearls were naturally polished and did not need to be cut; they could be mounted on jewelry or strung as beads. Some rivers in Scotland, of all places, contained mussels that made small pearls. But the finest pearls, and by far the most, came from outside Europe. The Mediterranean coast along North Africa had pearl beds, and the Persian Gulf had even more. The Crusader kingdoms spurred increased importation of pearls into Europe.