The open encyclopedia of minerals
GlossaryCite the database
Mineralogist.org
Minerals A–ZSearchCollectionsBrowse by PropertyIdentify a SpecimenCompare MineralsLocalities MapGlossaryContribute Search the Database →
Mineral group · Silicate · Cyclosilicate (ring silicate) — borosilicate · Tourmaline Group

Tourmaline

(Na,Ca)(Mg,Fe,Li,Al)₃Al₆(BO₃)₃Si₆O₁₈(OH)₄

Not one mineral but a whole supergroup — boron-rich cyclosilicates that come in more colors than any other gemstone family.

Hardness7–7.5
Crystal systemTrigonal
LusterVitreous
Sp. gravity2.9–3.3
ClassSilicate
←PrevTounkiteNextTownendite→
Tourmaline specimen

Tourmaline — the boron cyclosilicate supergroup behind dozens of species — Photo: James St. John · CC BY 2.0

What is Tourmaline?

Tourmaline isn't a single mineral — it's a supergroup of closely related boron-bearing cyclosilicates sharing one crystal structure. The general formula is written XY₃Z₆(T₆O₁₈)(BO₃)₃V₃W: the letters are crystallographic sites, and whichever elements dominate those sites decides the species. The International Mineralogical Association recognizes roughly forty tourmaline species.

The members you'll actually meet are few. Schorl — black, iron-rich — makes up the vast majority of all tourmaline and bristles through pegmatites and schists worldwide. Elbaite, the lithium-rich member, supplies nearly every gem color: green verdelite, blue indicolite, red-to-pink rubellite, color-zoned 'watermelon', and the copper-charged neon blues of Paraíba. Dravite is the brown magnesium member common in marbles, and uvite and fluor-liddicoatite fill out the calcium branch.

The structure is built from six-membered rings of SiO₄ tetrahedra with triangular BO₃ groups — the boron is the fingerprint: if a hard, striated, triangular-prism crystal turns up in a pegmatite, tourmaline is the first guess.

In one sentence: Tourmaline is hard (7–7.5), grows as deeply striated prisms with a rounded triangular cross-section, shows strong pleochroism, and is both pyroelectric and piezoelectric.

Physical Properties

The full data table is in the panel alongside. Here’s what those numbers actually mean.

One structure, many chemistries. All tourmalines share the same trigonal R3m framework. Mineralogists split the supergroup by what occupies the X site: alkali tourmalines carry Na (schorl, elbaite, dravite, olenite, tsilaisite), calcic tourmalines carry Ca (uvite, fluor-liddicoatite), and X-vacant tourmalines leave the site largely empty (foitite, rossmanite, magnesio-foitite).

Color and pleochroism. A tourmaline crystal is far darker viewed down its length than across it — cutters orient rough so the richest color faces up. Zoned crystals stack pink cores inside green rinds ('watermelon').

Electric personality. Tourmaline is hemimorphic — the two ends of a crystal develop differently — so heating or squeezing it builds opposite charges at opposite ends. Warmed crystals famously attract ash and dust; Victorian shops sold 'tourmaline tongs' to demonstrate it.

Members

Same chemistry, different faces — trace impurities and how finely it crystallizes give a whole family of familiar stones.

Schorl
Schorl
Black · Iron-rich (Fe²⁺)
Elbaite
Elbaite
All gem colors · Lithium + aluminium
Dravite
Dravite
Brown · Magnesium-rich
Uvite
Uvite
Dark brown to green · Calcium + magnesium
Fluor-liddicoatite
Fluor-liddicoatite
Zoned multicolor · Calcium + lithium
Olenite
Olenite
Pink · Aluminium-rich, Na site
Foitite
Foitite
Black to blue-black · Fe²⁺ with vacant X site
Tsilaisite
Tsilaisite
Yellow-brown to pink · Manganese-rich (Mn²⁺)
Rossmanite
Rossmanite
Pale pink · Lithium + Al, vacant X site

How & Where It Forms

Tourmaline is the signature mineral of boron-rich granitic pegmatites — late-stage melts where boron, lithium and other rare elements concentrate and crystallize into giant pockets. Dravite and uvite favor metamorphosed dolomitic marbles; schorl is widespread in schists and gneisses. Because it resists weathering, gem tourmaline also accumulates in river gravels.

Often grows alongside:

QuartzFeldsparLepidoliteBerylMuscoviteSpodumene

What It’s Used For

GemstonesOctober birthstone. Rubellite, indicolite, verdelite, watermelon and neon Paraíba elbaite are the famous gem faces.
Piezoelectric & pyroelectricPressure or heat on a crystal produces a voltage — tourmaline plates once served in depth gauges and 'tourmaline tongs' polariscopes.
Collector specimensStriated prisms with triangular cross-sections and color-zoned terminations are among the most displayed minerals.

How to Identify It

Look for long prisms with a triangular, 'Mercedes-star' cross-section and heavy vertical striations. Hardness 7–7.5 with no real cleavage, strong color shift on rotation, and (for the curious) a warmed crystal that picks up dust clinch it.

Prisms with a rounded triangular cross-section and heavy lengthwise striationsHardness 7–7.5 — scratches quartz barely, no good cleavageStrong pleochroism: rotate a crystal and the color visibly shiftsPyroelectric — warming makes the crystal ends attract dust
Looks like…But differs because…Quick test
BerylSix-sided prisms, weaker pleochroism, lighter (SG ~2.7) — tourmaline is triangular in cross-sectionCross-section shape
QuartzQuartz prisms are six-sided and uniaxial (+); tourmaline is darker down the c-axis and often has a green or black corePleochroism & habit
ApatiteMuch softer (5) and hexagonal — a knife scratches apatite, not tourmalineHardness
AmphiboleBlack hornblende has two strong cleavages at ~120°; schorl lacks them and shows a triangular sectionCleavage check

Where It’s Found

Notable localities for fine specimens:

Minas Gerais pegmatites, Brazil São José da Batalha, Brazil Island of Elba, Italy Pala, USA Mogok, Myanmar Dunton Quarry, Newry, USAOpen the locality map →

References & Further Reading

  1. Henry, D.J., et al. (2011) Nomenclature of the tourmaline-supergroup minerals. American Mineralogist 96, 895–913.
  2. Dana's New Mineralogy, 8th ed. Tourmaline group, cyclosilicates.
  3. Mindat.org — Tourmaline supergroup mineral data and locality records.
  4. Wikipedia — Tourmaline.

Last reviewed 2026-09-14 · How to cite this page.