Tourmaline
Tourmaline isn’t a single mineral species but a group of closely related boron-silicate minerals with genuinely variable composition, which is why no single chemical formula applies across the board. Most gem-quality tourmaline belongs to the species elbaite, a lithium-rich member of the group, but the tourmaline family more broadly includes other compositions as well — a structural fact that, as with garnet, means “tourmaline” functions in the trade more like a family name than a strict species label.
What that chemical variability produces is arguably the widest color range of any major gemstone: tourmaline occurs in vivid pink, green, blue, yellow, and virtually every shade between, sometimes within a single crystal. The best-known example is “watermelon tourmaline,” which shows a pink core surrounded by a green rim, cut in cross-section to display both colors at once — a direct visual result of the crystal’s chemistry changing as it grew. Paraíba tourmaline, a vivid, copper-colored blue-green variety first found in Brazil in the late 1980s, is among the most valuable colored gems in the world today.
Brazil remains a major source across many tourmaline colors, alongside Nigeria, Mozambique, Afghanistan, Madagascar, and the United States (notably Maine and California, historically significant sources of fine pink and green material). At Mohs 7 to 7.5, tourmaline is durable enough for regular wear, similar to quartz in scratch resistance, and needs no unusual care beyond standard cleaning and avoiding harsh chemicals. It also carries a strong electrical property worth mentioning for context rather than jewelry care: tourmaline is pyroelectric and piezoelectric, generating a small electrical charge when heated or under pressure, a trait early mineralogists noted long before its gem qualities were fully appreciated.
Tourmaline’s birthstone role is a secondary one and a relatively recent addition: it’s paired with opal for October on both the US 1912 list and the current US list, but it’s absent from the historical October entry (opal and aquamarine) and from the UK 2013 list (opal alone). It doesn’t appear on either zodiac birthstone system tracked here. Its position — present on two of four monthly lists, always as a second stone rather than the headline gem — makes it a useful example of how birthstone lists accumulate additions over time rather than staying fixed once set.
Gemmological properties
| Mohs hardness | 7–7.5 |
|---|---|
| Crystal system | Trigonal |
| Chemical formula | Not recorded |
| Refractive index | 1.624–1.644 |
| Color family | Multicolour, Green, Pink, Blue |
| Variety of | — |
| Also known as | — |
| Origins | Brazil, Nigeria, Mozambique, Afghanistan, United States, Madagascar |
| Organic material | No |
Tourmaline is a mineral group with complex, variable boron-silicate chemistry — gem material is usually the lithium-rich species elbaite — so no single formula applies to the whole group.
Where Tourmaline appears as a birthstone
By month
Frequently asked questions
- Why doesn't tourmaline have a single chemical formula?
- Because it isn't one mineral — it's a group of closely related boron-silicate minerals with genuinely variable chemistry across the group. Most gem-quality tourmaline is the lithium-rich species elbaite, but the group also includes other members with different compositions, which is why gemological references give a range rather than a single formula.
- Is tourmaline really the most color-varied gemstone?
- It has a strong claim to it. Tourmaline occurs naturally in nearly every color, including bicolor and even tricolor crystals within a single stone (the 'watermelon' variety, with a pink center and green rim, is the best-known example) — a range broader than most single gem species show.
- Where does tourmaline appear as a birthstone?
- It's a secondary October stone on the US 1912 and current US lists, alongside opal, but it doesn't appear on the historical or UK 2013 October entries, or on either zodiac system tracked here.