GEMSTONE FIELD GUIDE
Tourmaline
Tourmaline is a chemically variable mineral supergroup with solid-solution relationships. Elbaite and dravite are examples, not an exhaustive species list. Color names do not by themselves establish a mineral species. This record is a common-gem overview, not universal supergroup bounds.
A selection of faceted tourmalines in several colors.
Tourmaline spans several mineral species and many colors. Color alone cannot determine the species of each pictured stone.
Michelle Jo / Public domain, via Wikimedia Commons · Source ↗ · Public domain · resized for the webA verified 3D specimen capture is not available for this entry. No generated stand-in is used.
AT A GLANCE
Start with the evidence.
Tourmaline covers multiple mineral species and many color names. A color label does not establish species, copper content, geographic origin or whether the whole object is tourmaline.
- Refractive index (RI)
- 1.624–1.644
- Specific gravity (SG)
- 3.00–3.26 · typical 3.06
- Mohs hardness
- 7–7.5
simplified common-gem reference interval
How to read this value
GIA headline interval. Composition and species matter; for example, the Handbook's elbaite principal-index populations extend beyond it. Do not use the interval as a hard pass/fail boundary or as the readings of every stone.
How to read this value
Arithmetic expansion of GIA's 3.06 (+0.20, −0.06), for its gem-tourmaline overview. Not comprehensive bounds for the supergroup.
How to read this value
Scratch resistance, not toughness. This ordinal scale is not linear.
These are reference properties, not measurements of the pictured specimen. Reference images are educational—not NumisTrends sale inventory.
See the details and limitations ↓01 · IDENTIFY
Build a profile, not a guess.
Typical material-level reference; not a measurement, identification, origin, treatment determination, or grading result for any specimen.
Refractive index (RI)1.624–1.644
simplified common-gem reference interval
GIA headline interval. Composition and species matter; for example, the Handbook's elbaite principal-index populations extend beyond it. Do not use the interval as a hard pass/fail boundary or as the readings of every stone.
Specific gravity (SG)3.00–3.26 · typical 3.06
Arithmetic expansion of GIA's 3.06 (+0.20, −0.06), for its gem-tourmaline overview. Not comprehensive bounds for the supergroup.
Mohs hardness7–7.5
Scratch resistance, not toughness. This ordinal scale is not linear.
Birefringence0.018–0.040
GIA common-gem reference, not a value shared by all tourmaline species. Population RI endpoints are not a specimen's measured birefringence.
Optic characterNormally uniaxial negative
Elbaite's mineral reference corroborates negative uniaxial character and notes strain-induced slight biaxiality.
CleavageVery poor / generally not a prominent practical cleavage
Handbook elbaite has very poor cleavage. Do not assume identical expression in every tourmaline species or confuse fractures with cleavage.
Open a property for its scope and source. RI and specific gravity have no units. Mohs describes scratch resistance—not resistance to breaking. Do not scratch a stone to test it.
What can look similar?
Manufactured glass resembling Paraíba tourmaline
Blue-green glass can be shaped as a prism and contain metallic inclusions.
How to investigate. Microscopy and optical measurements, with infrared confirmation if needed, distinguish the documented glass.
The resemblance is visual; the material is not synthetic tourmaline.
Tourmaline-crown and glass-pavilion doublet
A real tourmaline crown can give tourmaline-consistent readings while hiding a glass base.
How to investigate. Examine the full construction under magnification, not only the crown.
A genuine component does not make the assembled object solid tourmaline.
02 · TESTS & ULTRAVIOLET
What a test can—and cannot—tell you.
Results depend on the specimen, instrument and method. This is a reference for understanding evidence, not a home authentication or treatment verdict.
UV reaction
- Long-wave UV
- The tourmalines studied from Luc Yen, Vietnam, were inert under longwave UV.
- Short-wave UV
- Within that study, some green, yellow and brownish-yellow specimens fluoresced yellowish green; pink, red, brown and black samples were inert.
This describes the study's material, not all tourmaline species or a color-based prediction for another stone. Fluorescence alone cannot determine species, treatment or geographic origin.
Optical properties plus microscopy
Whether the object is tourmaline rather than a convincing imitation.
Reference observation. GIA's crystal-shaped glass imitations had optical properties and internal glass features inconsistent with tourmaline.
Limit. Crystal-like outlines and metallic-looking inclusions are not proof of natural growth.
Component-specific spectroscopic identification
Whether different parts of an assembled object are different materials.
Reference observation. Raman identified a tourmaline base beneath an amethyst cabochon in a documented doublet.
Limit. One surface reading does not identify the entire object. Keep each component's result separate.
Real laboratory examples
Documented cases, not test results of the reference specimens shown on this page.
A laboratory case of glass dressed as a crystal
GIA examined two bluish-green glass prisms with copper inclusions. Fused regions, gas bubbles and flow structures exposed their manufactured construction; infrared spectroscopy confirmed glass.
The takeaway. A rough-looking crystal can still require the same material checks as a polished gem.
Use a qualified gemologist for identification work. Do not expose eyes or skin to UV sources, or perform scratch, heat, acid or solvent tests on a gemstone. Do not assume that an absent UV reaction rules a material out.
03 · TREATMENTS & CARE
Protect the stone you actually have.
Disclosed treatments, fractures and settings can change which cleaning methods are appropriate.
Use warm soapy water rather than steam or ultrasonic cleaning. Protect against thermal shock and high heat. Some irradiation-produced colors can fade under heat or bright light.
04 · SOURCES & SCOPE
Know where each fact comes from.
Original NumisTrends explanations with primary references. This is not a replacement for gemological training, a laboratory report, or the examination of your own stone.
Properties reviewed: 2026-09-07 · Identification notes reviewed: 2026-09-07
NumisTrends is independent of GIA, Gem-A and the museums cited. A matching property cannot by itself establish identity, natural versus laboratory-grown origin, treatment, geographic origin, grade or value.