Yellow Topaz

Topaz is an aluminium fluorosilicate, a hard stone at 8 on the Mohs scale but with one perfect cleavage that makes it liable to split, and yellow to golden-brown is its classic historical colour, imperial topaz is the prized pinkish-golden grade. A caution runs through its history: the ancient name topazos, said by Pliny to come from an island in the Red Sea, was applied to yellow-green stones that were probably peridot, not topaz, so much topaz in classical and medieval sources is another mineral, and conversely many yellow gems called topaz in old jewellery are citrine quartz. True topaz was securely distinguished only in the modern era. It is a November birthstone. Much blue topaz in today's market is colourless material turned blue by irradiation. Its metaphysical associations, solar and abundance-themed for the yellow stones, are modern and colour-led.

Medieval and Renaissance lapidaries repeat a persistent claim that a genuine topaz would grow visibly dimmer in the presence of poison and recover its brilliance once the danger passed, a belief with no basis in the stone's actual optical or chemical properties but repeated across centuries of gem-lore as a mark of the stone's protective virtue. The confusion of topaz with other yellow stones, noted above from Pliny, persisted into the modern era: the Braganza, a colourless 1,680-carat stone long displayed among the Portuguese crown jewels and believed for generations to be the largest diamond ever found, was eventually identified as topaz, a correction that embarrassed collectors well into the nineteenth century.

Topaz has one property that governs how it can be used and one deposit that governs what the best of it looks like.

The property is perfect basal cleavage. Topaz splits cleanly along a single plane at right angles to the long axis of the crystal, and a sharp knock in the wrong direction will part a finished stone in two. Cutters orient the table slightly off the cleavage plane to reduce the risk, setters handle it carefully, and topaz is a poor choice for a ring that will be worn daily. That is a mineralogical fact with direct consequences for the objects that survive.

The deposit is Ouro Preto in Minas Gerais, Brazil, the source of the orange to reddish material sold as imperial topaz, which is the most valuable colour the species produces. The name is a trade term of the nineteenth century and is applied loosely; the atlas records it as such.

Topaz also holds a curious record. Because the mineral occurs in very large, clean, colourless crystals in pegmatites, some of the largest faceted gemstones in the world are topaz, running to thousands of carats. They are cut because the rough exists, not because anyone needed them.

Most blue topaz on the market is colourless topaz that has been irradiated and then heated. The treatment is stable, it is inexpensive, and it is the reason blue topaz went from rare to ubiquitous in the later twentieth century. Untreated natural blue topaz is pale and uncommon, and the intense blues in a shop window are not what the stone does on its own.