Tourmaline Identification Guide
Identify tourmaline by its striated three-sided prisms, rounded-triangular cross-section, strong pleochroism, and tests against beryl and quartz.
Read the full Tourmaline encyclopedia entry →
What Tourmaline Looks Like
Tourmaline is a complex boron silicate group occurring in nearly every color, sometimes several in one crystal.
- Color: every color — green (verdelite), pink/red (rubellite), blue (indicolite), black (schorl), and bicolor 'watermelon'
- Luster: vitreous
- Transparency: transparent to opaque
- Form: elongated prismatic crystals with strong lengthwise striations and a distinctive rounded triangular cross-section (trigonal); often vertically grooved like a soda straw
Step-by-Step Field ID Checklist
- Look for long, striated prisms with deeply grooved faces parallel to the length.
- Check the cross-section: a rounded triangle (curved-sided) is highly diagnostic of tourmaline.
- Rotate a transparent crystal for strong pleochroism — color visibly darkens or shifts along vs across the length.
- Note color zoning (concentric or end-to-end), common in tourmaline.
- Confirm hardness scratches glass.
Key Diagnostic Tests
- Hardness: ~7–7.5 (scratches glass and quartz weakly).
- Streak: white to colorless (even black schorl gives a pale streak).
- Cleavage: essentially none — uneven to conchoidal fracture.
- Pleochroism: strong, a key gem-test feature.
- Pyro/piezoelectricity: crystals can attract dust/paper when warmed or rubbed (classic tourmaline test).
- Density: ~3.0–3.3.
Common Look-Alikes
- Beryl (emerald, aquamarine): hexagonal with flat-sided prisms and a hexagonal cross-section, weaker pleochroism, lower density; tourmaline's curved triangular section differs.
- Quartz (amethyst, citrine): hexagonal prisms with horizontal striations and a pointed termination; tourmaline striations run lengthwise.
- Andalusite/peridot: different habits; peridot is olive only and has strong doubling.
- Glass: no pleochroism, no striations, may show bubbles.
- Schorl vs black hornblende/augite: hornblende has good cleavage; tourmaline lacks cleavage and shows the triangular section.
Striated triangular-section prisms + strong pleochroism + no cleavage identifies tourmaline.
Where It Is Found
Top sources include Brazil (Minas Gerais, including Paraíba), Afghanistan, Pakistan, Nigeria, Mozambique, Madagascar, and the USA (California, Maine). Tourmaline crystallizes mainly in granitic pegmatites and metamorphic rocks.
Frequently asked questions
How can you tell if a crystal is tourmaline?
Tourmaline forms long prisms with strong lengthwise striations and a rounded triangular cross-section, shows strong pleochroism, has hardness 7–7.5, no cleavage, and can attract dust when warmed.
Tourmaline vs beryl: what's the difference?
Beryl (emerald, aquamarine) has a hexagonal cross-section and flat prism faces, while tourmaline has a distinctive curved triangular cross-section with deep lengthwise grooves and stronger pleochroism.
What does raw tourmaline look like?
Raw tourmaline appears as elongated, vertically striated three-sided prisms, often vividly colored or color-zoned end-to-end, and may show black, green, pink, blue, or multicolor 'watermelon' zoning.
Does tourmaline have cleavage?
No, tourmaline has essentially no cleavage and breaks with an uneven to conchoidal fracture, which helps separate it from cleavable look-alikes like hornblende and feldspar.
Tourmaline identified by the community
Recent Tourmaline specimens identified with Rock Identifier.
