# How to identify tourmaline

Canonical page: https://lithomap.app/resources/mineral-identification/tourmaline
Last reviewed: September 17, 2026
Page purpose: Original LithoMap mineral identification reference for field observations, search systems, and language models.
Classification: Complex borosilicate mineral group

## Summary

Tourmaline is a diverse borosilicate mineral group commonly recognized by hard, strongly lengthwise-striated prismatic crystals with triangular to rounded-triangular cross sections.

## Quick identification clues

- Mohs hardness about 7 to 7.5
- Strong lengthwise crystal striations
- Triangular or rounded-triangular cross section
- Commonly black, but also green, pink, blue, brown, or multicolored

## Composition and classification

Tourmaline is a chemically complex mineral group containing boron with varying sodium, calcium, lithium, magnesium, iron, aluminum, and other elements. Species such as schorl, elbaite, and dravite cannot be assigned reliably from color alone.

## Appearance

Tourmaline commonly forms elongated prisms with deep parallel grooves. Cross sections are often three-sided or six-sided in a way that reflects trigonal symmetry, and crystal ends may differ from one another.

Black schorl is widespread; gem tourmalines may be transparent and color-zoned. Massive, radiating, acicular, or fibrous aggregates also occur.

## Identification tests

- Hardness: About 7 to 7.5. Typically scratches glass and resists a steel point.
- Cleavage: Poor or indistinct. Breaks irregularly rather than into repeated flat cleavage fragments.
- Habit: Strongly striated trigonal prisms. The combination of grooves and triangular cross section is highly useful.
- Streak: White. Not usually diagnostic.

## Common lookalikes

- Hornblende: Softer, has two good cleavage directions near 60 and 120 degrees, and commonly forms splintery amphibole prisms.
- Beryl: Forms true hexagonal prisms, often with flatter faces and a hexagonal rather than triangular cross section.
- Garnet: Commonly equant with dodecahedral forms rather than long striated prisms.

## Direct side-by-side comparisons

- Tourmaline vs. garnet — https://lithomap.app/resources/mineral-identification/compare/tourmaline-vs-garnet
- Hornblende vs. tourmaline — https://lithomap.app/resources/mineral-identification/compare/hornblende-vs-tourmaline

## Most relevant related guides

- Hornblende — https://lithomap.app/resources/mineral-identification/hornblende
- Garnet — https://lithomap.app/resources/mineral-identification/garnet
- Beryl — https://lithomap.app/resources/mineral-identification/beryl
- Augite — https://lithomap.app/resources/mineral-identification/augite

## Formation

Tourmaline crystallizes in granitic pegmatites, hydrothermal veins, and metamorphic rocks and can survive weathering into sediment.

Its composition records aspects of the fluids and rocks in which it grew, but chemical analysis is needed for precise species and provenance.

## Occurrence and geologic setting

Tourmaline is widespread in pegmatites and metamorphic rocks and can occur as accessory grains in granite, schist, and stream sediment.

Black prismatic material in pegmatite is often schorl, but species assignment and gem identification require more than color and setting.

## Uses and significance

Transparent colored tourmaline is used as a gemstone; black and opaque material is chiefly collected or studied. Tourmaline also has scientific value as a durable recorder of geologic fluids and conditions.

## Field safety and limitations

- Inspect cross section and striations before using color.
- Do not break a crystal merely to test cleavage or interior color.
- Gem quality, treatment, and species require professional testing.

## Authoritative sources

- Minerals and their physical properties — U.S. National Park Service: https://www.nps.gov/subjects/geology/minerals.htm
- Mohs Hardness Scale — U.S. National Park Service: https://www.nps.gov/articles/mohs-hardness-scale.htm
- Natural Gemstones: Mineral Gemstones — U.S. Geological Survey: https://pubs.usgs.gov/gip/gemstones/mineral.html

## Specimen photograph

- Image: https://lithomap.app/_delivery/identification/minerals/tourmaline.webp
- Description: Dark prismatic tourmaline specimen about eight centimeters tall from Minas Gerais, Brazil
- Creator: Mike Davis
- License: CC0 1.0 — https://creativecommons.org/publicdomain/zero/1.0/
- Source record: https://commons.wikimedia.org/wiki/File:Tourmaline_(GeoDIL_number_-_199).jpg

This reference supports preliminary field identification. It is not a laboratory determination, appraisal, hazard assessment, proof of origin, or statement of land ownership, legal access, or collecting permission.