Black Tourmaline
“Tourmaline” is a group name, not a single mineral, and this site’s tourmaline entry deliberately doesn’t give one chemical formula for that reason — the group covers a range of related minerals whose chemistry shifts along several axes at once. Black tourmaline sidesteps that ambiguity because it isn’t the group; it’s one specific, well-defined member of it: schorl, the iron-rich end member. Where iron dominates the composition, in place of the magnesium, lithium, or other elements that define the group’s other members, the result is schorl, with a genuinely fixed formula, NaFe3Al6(BO3)3Si6O18(OH)4, and a genuinely fixed color: black, essentially without exception.
That specificity is worth dwelling on, because it’s the opposite situation from smoky quartz or amethyst, where one species shows up in many colors. Tourmaline works the other way: different chemistry produces different named varieties, and schorl’s particular iron-rich chemistry is what pins its color down to black rather than leaving it variable. Pink rubellite, green verdelite, and the parti-colored watermelon tourmaline are other points on the same compositional spectrum, each defined by a different dominant element.
Schorl is also, despite the specialty status “black tourmaline” tends to carry in jewelry listings, the single most common tourmaline species by a wide margin. Most tourmaline found in nature — in granite, pegmatites, and metamorphic rocks worldwide — is schorl. The vividly colored gem varieties that dominate people’s mental image of tourmaline are the statistical exception, not the rule; schorl is the abundant baseline they’re carved out from.
At Mohs 7 to 7.5, schorl is durable enough for everyday jewelry, with a refractive index around 1.63 to 1.68, both figures broadly consistent with the tourmaline group as a whole. Major sources include Brazil, Pakistan, Afghanistan, the United States, and Madagascar, with crystals often occurring as long, striated prisms embedded in granite and pegmatite.
Because it forms so readily and so abundantly, schorl also turns up as an incidental inclusion in other minerals — needle-like schorl crystals are a common inclusion in quartz, sometimes forming striking black-on-clear specimens that are collected in their own right rather than cut as gems.
Black tourmaline doesn’t appear on any of the historical or modern monthly birthstone lists, or on either zodiac system, tracked on this site — it’s included here as a standalone reference entry, the same way malachite is.
Gemmological properties
| Mohs hardness | 7–7.5 |
|---|---|
| Crystal system | Trigonal |
| Chemical formula | NaFe3Al6(BO3)3Si6O18(OH)4 |
| Refractive index | 1.63–1.68 |
| Color family | Black |
| Variety of | tourmaline |
| Also known as | Schorl |
| Origins | Brazil, Pakistan, Afghanistan, United States, Madagascar |
| Organic material | No |
Unlike the tourmaline group entry on this site, black tourmaline is one specific member — schorl, the iron-rich end of the group — which is why it can carry a definite formula where the parent group entry cannot. Schorl is by far the most abundant tourmaline; the colored gem varieties are the rarity.
Frequently asked questions
- Is black tourmaline the same thing as the tourmaline group?
- No — it's one specific member of that group. 'Tourmaline' names a family of related minerals that share a crystal structure but vary in chemistry and color, which is why this site's tourmaline group entry deliberately doesn't give a single formula. Black tourmaline is specifically schorl, the iron-rich end member, and because its composition is defined, it can carry a formula the parent group entry cannot.
- Is schorl rare?
- No — it's the opposite. Schorl is by far the most common tourmaline species, making up the large majority of tourmaline found in nature. The colored gem varieties people usually picture when they hear 'tourmaline' — pink, green, blue, watermelon — are comparatively rare; black schorl is the abundant baseline the rarer varieties are exceptions to.
- Is black tourmaline a birthstone on any of the lists this site tracks?
- No. It doesn't appear on any of the historical, US, UK, or zodiac systems documented on this site — it's covered here as a standalone gemstone reference entry.