Crystal guide
How to Identify Tourmaline
Complex borosilicate group
Tourmaline is a borosilicate gem group forming striated trigonal prisms in virtually every color, famous for watermelon zoning. Identify it by strong pleochroism (two colors by angle), Mohs 7–7.5, fluted prism sides, and pyroelectric dust attraction when warmed.
About Tourmaline
Tourmaline is a borosilicate gem group forming striated trigonal prisms in virtually every color, famous for watermelon zoning. Identify it by strong pleochroism (two colors by angle), Mohs 7–7.5, fluted prism sides, and pyroelectric dust attraction when warmed.
Tourmaline is filed under crystals in the RockScan directory. Composition: Cyclosilicate borosilicates (elbaite, schorl, etc.). It forms via pegmatites and metamorphic rocks. Typical occurrence: Brazil, Afghanistan, Nigeria, Mozambique, USA. For the broader method, see how to identify rock types.
Tourmaline properties
| Mohs hardness | 7–7.5 |
|---|---|
| Class | crystal |
| Scientific name | Complex borosilicate group |
| Color | All colors; watermelon zoning common |
| Luster | Vitreous |
| Crystal system / texture | Trigonal |
| Composition | Cyclosilicate borosilicates (elbaite, schorl, etc.) |
| Formation | Pegmatites and metamorphic rocks |
| Occurrence | Brazil, Afghanistan, Nigeria, Mozambique, USA |
How to identify Tourmaline
- Striated three-sided prisms; color shifts with viewing angle (pleochroism).
- Mohs 7–7.5; watermelon pink-green zoning common.
- Warm crystals attract dust (pyroelectricity) — glass never does.
Lookalikes to rule out
- Peridot: Peridot shows strong facet doubling with no pleochroism; tourmaline shows strong pleochroism with striated trigonal prisms.
- Emerald: Emerald is beryl with jardin inclusions and a chromium spectrum; green tourmaline is softer-birefringent with tube inclusions and pleochroism.
- Glass: Glass lacks pleochroism and shows bubbles; tourmaline shifts color with viewing angle and grows striated prisms.
Photo tips for Tourmaline ID
- Shoot color change with rotation — pleochroism on camera is tourmaline's best proof.
- Capture striated trigonal prisms lengthwise; the fluted sides are diagnostic.
- Show watermelon and multicolor zoning end-on; sliced tourmaline cross-sections are iconic.
Snap one specimen in natural light, then open the result in the online studio or the rock identifier app.
Tourmaline FAQ
How do you identify tourmaline?
Rotate striated prisms and watch color shift — strong pleochroism plus fluted trigonal sides marks tourmaline. Glass and peridot behave differently.
Tourmaline vs emerald?
Emerald is beryl with garden inclusions; green tourmaline shows pleochroism, tube inclusions, and trigonal prisms.
What is watermelon tourmaline?
Pink-core, green-rind zoned crystals sliced crosswise — the group's most photographed variety, from pegmatite pockets.
How to identify tourmaline
No gem shifts color with angle quite like tourmaline. Rotation plus prism shape replaces guesswork:
- Pleochroism: two distinct colors (dark/light pair) as you rotate — photograph both angles.
- Fluted prisms: deeply striated three-sided sides, unlike smooth beryl or glass.
- Zoning: watermelon rinds, color-blocked ends, and striped pockets from pegmatite growth.
- Hardness 7–7.5: scratches quartz; softer copper greens (chrysocolla) gouge far easier.
- Photo confirm: rotation pair plus prism-side macro, then RockScan against peridot and emerald-type greens.
Tourmaline vs peridot vs emerald vs glass
- Peridot: facet doubling instead of pleochroism, in pure yellow-green olivine.
- Emerald: beryl optics with jardin gardens; tourmaline shows tubes and stronger angle shift.
- Glass: one static color with bubbles; no pleochroism, striations, or zoning.
Photo tips for tourmaline pleochroism
Shoot the same prism at two rotations to freeze the color shift, plus an end-on zoning slice. Compare peridot, aquamarine, and pegmatite guides, then confirm in the online studio or rock identifier app.
Related crystals to compare
Browse all: rocks · minerals · crystals · directory · what rock is this · rock vs mineral vs crystal. Confirm with the online studio or rock identifier app.