Where tourmaline actually comes from

The classical source, and still the one that sets the reference for quality. Minas Gerais produces rubellite, indicolite, verdelite and bi-colour material from the Cruzeiro and Araçuaí pegmatites. The Batalha mine at São José da Batalha, in Paraíba state, produced the original copper-bearing material from 1989 and is now effectively exhausted; what circulates is old stock.

The dominant commercial source of cuprian tourmaline today, worked largely by artisanal miners over roughly three square kilometres of alluvial ground. The material is waterworn rather than crystalline, generally cleaner and larger than Brazilian, and — by GIA's account of the deposit — only about a tenth of what is dug shows the neon colour that carries the name.

The third commercial source of copper-bearing tourmaline, from the Edoukou area of Oyo State, alongside large quantities of pink, green and bi-colour material across the Pan-African pegmatite belt. Production is artisanal and expanding rather than declining, and the geological mapping is thin: much of the belt has never been surveyed properly. Export now requires documentation, and most material has historically left the country informally.

Well-formed, sharply terminated prisms with strong striations, often in pink, green and bi-colour. This is the material most likely to be sold as a mineral specimen rather than as facet rough, and the habit is distinctive enough to be a useful origin clue on a crystal.

The classic source of liddicoatite — the calcium-lithium species whose triangular polished slices, with concentric colour zoning, are often mislabelled as elbaite. Also produces gem elbaite in a wide colour range.

Mount Mica in Maine was the first commercial gem mine in the country, worked from 1820. The San Diego County pegmatites — the Himalaya mine above all — supplied pink tourmaline to the Chinese imperial court in the 1890s, a market that collapsed with the dynasty in 1912. Both districts still produce on a small scale.

Namibia produces fine indicolite and darker blue-green material from the Erongo region. East African chrome tourmaline, coloured by chromium and vanadium, comes chiefly from Tanzania and rarely exceeds a few carats clean.

Historically the most important source of all, in the sense that matters here: it is where the name came from. Ceylonese traders called the assorted coloured stones in their parcels turmali, and Dutch merchants carried both the stones and the word to Europe in the early 1700s.