How to tell if tourmaline is real
Real tourmaline looks darker down its length and gives two refractometer readings about 0.020 apart, near 1.62 to 1.67. Glass gives one. Hardness 7 to 7.5.
To tell if tourmaline is real, look at it end-on, then use a refractometer. Real tourmaline is darker looking down its length than across it (IGS), and gives two readings between about 1.62 and 1.67, usually around 0.020 apart. Glass gives one reading. Hardness is 7 to 7.5. No lab-grown tourmaline is sold commercially.
In short
- Tourmaline is a group, so real means any tourmaline species. GIA says most gem tourmalines are elbaite; black crystals are usually labelled schorl. The Handbook of Mineralogy sheets give hardness 7 and density 2.90 to 3.10 for elbaite and 3.18 to 3.22 for schorl. A fake is glass, another gem, or a tourmaline sold under a name it does not deserve.
- The end-on check costs nothing. The International Gem Society says single colours are always stronger down the c axis: light travelling along a prism shows a deeper colour than light across it. A tourmaline cut with its length face-up can look forest green from the top and olive from the side. Glass, being singly refractive, shows no such change.
- The gap-and-position rule: two refractometer readings, both between about 1.61 and 1.70, at least 0.013 apart, fit tourmaline. Quartz reads 1.544 and 1.553, 0.009 apart. The calcium apatites sit in the same window as tourmaline but, on the gem society's figures, at most 0.008 apart, francolite aside. Glass gives one reading.
- One reading does not always mean glass. The IGS notes that a dark tourmaline can absorb one ray totally and show a single line. That is why the rule has a second half, position: a single line near 1.49 is obsidian territory, and a single line above 1.62 needs the end-on check and the scale.
- Synthetic tourmaline is not the usual problem. The IGS says no lab-created tourmaline is commercially available for jewellery, and that simulated tourmaline usually means a fake. Treatments are common: heating, irradiation and fillers. Paraíba origin and treatment questions go to a gem laboratory.
| Reading on the refractometer | Gap between readings | Source numbers | Points to | Next step |
|---|---|---|---|---|
| Two readings, both about 1.61 to 1.70 | 0.013 or more | IGS: elbaite 0.013 to 0.024, dravite 0.016 to 0.032, schorl 0.016 to 0.046, uvite 0.017 to 0.021, liddicoatite 0.016 | Tourmaline | End-on check; treatment and origin are laboratory questions |
| Two readings, 1.544 and 1.553 | 0.009 | Handbook quartz sheet | Quartz | See is tourmaline a quartz |
| Two readings near 1.63 to 1.67 | Under 0.010 | IGS: chlorapatite about 0.001, fluorapatite 0.004, hydroxylapatite 0.007, carbonate apatites to 0.008 | Apatite | Hardness 5 against 7, on rough only |
| One reading, 1.470 to 1.700 | None | IGS glass: singly refractive, often anomalous double refraction | Glass | Lens: round bubbles, swirl marks |
| One reading, 1.48 to 1.51, on a black stone | None | IGS obsidian: isotropic, usually 1.49 | Obsidian | See how to tell tourmaline from obsidian |
| One reading above 1.62 | None visible | IGS: the O ray can be totally absorbed, showing a single line | Possibly tourmaline | End-on check and the scale before calling it glass |
How to tell if tourmaline is real: six checks, in order
Start with your eyes and a lamp, and finish, if you need to, at a gem laboratory. The order runs from free and harmless to costly. The Handbook of Mineralogy sheet for elbaite and the schorl sheet give the numbers: hardness 7, uniaxial negative, density 2.90 to 3.10 for elbaite and 3.18 to 3.22 for schorl. Day one needs only a 10x lens and a single lamp.
- End-on and side-on. Look along the length of a crystal or a long stone, then across it. A deeper colour along the length is the tourmaline pattern the International Gem Society describes.
- 10x lens. Round bubbles and swirl marks mean glass. The IGS describes tourmaline's own inclusions as hollow tubes, typically running parallel to the length, and red tourmaline's as gas-filled fractures and flat films that look black under magnification.
- Crystal form, on rough. Every tourmaline sheet used here records a trigonal prism or triangular cross-section, and four of the five print striations parallel to the length. The comparison with quartz is on is tourmaline a quartz.
- Scale. A 20.00 g loose piece reads 13.10 to 13.55 g in water as elbaite and 13.71 to 13.79 g as schorl. The method is on how to measure specific gravity at home.
- Refractometer. Apply the gap-and-position rule in the table.
- Laboratory. For Paraíba-type copper colour, treatment or origin, nothing earlier on the list decides it.
The finish state is one of five labels: tourmaline; tourmaline, treatment or origin still open; glass; obsidian; or another gem such as quartz or apatite. The identification pages are indexed at the collecting guides, and the species background is on tourmaline.
Is my tourmaline real or glass? The gap-and-position rule
The gap-and-position rule: a stone that gives two readings between about 1.61 and 1.70, at least 0.013 apart, is behaving as tourmaline. The International Gem Society puts tourmaline's gap, its birefringence, usually around 0.020. Its species table gives elbaite 0.013 to 0.024, dravite 0.016 to 0.032, schorl 0.016 to 0.046, uvite 0.017 to 0.021 and liddicoatite 0.016. Of those five, elbaite has the lowest floor, 0.013, so that is the threshold used here. The Handbook sheets agree on position: elbaite's lowest index is 1.615, schorl's highest 1.671.
Each half of the rule rules something out. Position excludes quartz, whose two readings are 1.544 and 1.553 on its sheet, 0.062 below elbaite's lowest. The gap excludes the calcium apatites, which the IGS says can be hard to separate from faceted tourmaline because many properties overlap: their gaps run from about 0.001 to 0.008, with only the francolite variety reaching 0.013. Glass, on the gem society's figures, gives one reading anywhere from 1.470 to 1.700.
Where the rule needs help. The IGS says the absorption of one ray in tourmaline is sometimes strong enough to plane-polarise light, and at times it is totally absorbed, showing a single line. A single line above 1.62, then, is not proof of glass; the end-on check and the scale come back in. The same overlap is why glass and apatite are covered, briefly, on how to tell if a crystal is fake.
Is black tourmaline real? Black stones, beads and bracelets
Black tourmaline is usually schorl, and the schorl sheet gives it hardness 7, a white streak and density 3.18 to 3.22. The Handbook of Mineralogy sheet for schorl lists only black, brownish black and bluish black. Dravite and uvite sheets also list black, so a black tourmaline is a tourmaline before it is a schorl.
The black look-alikes are glass and obsidian. Both are singly refractive, and typical obsidian is much lighter in the hand; the worked numbers are on how to tell tourmaline from obsidian. On beads, the drill hole is a free window: in our judgement a lens at the hole shows whether the colour runs through the material or sits on the surface. The IGS lists dyes and coatings among tourmaline treatments and calls them usually unstable; the general method is on how to tell if a crystal is dyed.
Strung beads cannot be weighed one at a time, and a refractometer needs a polished flat, so a bracelet usually stops at the lens and the end-on check. That is an honest limit of home testing, not a verdict. This page gives no buying advice.
Is Paraíba, watermelon or pink tourmaline real? Names that need a laboratory
Watermelon is a colour pattern and Paraíba a copper colour; both can be real tourmaline, and only Paraíba needs a laboratory to confirm. GIA describes watermelon tourmaline as pink in the centre and green around the outside, usually cut in slices. It describes Paraíba as intense violetish blue, greenish blue or blue tourmaline from the state of Paraíba, Brazil. The International Gem Society says the gem community largely accepts a definition by colour and copper content, that some dealers reserve the name for Brazilian material, and that identifying the source requires quantitative chemical analysis.
The Handbook's elbaite sheet names the locality. Its Distribution field includes São José da Batalha, Paraíba, alongside the districts of Minas Gerais. The IGS adds that copper-bearing liddicoatites with Paraíba colours were discovered in 2017, so a Paraíba stone is not automatically elbaite.
Pink and red stones carry a treatment question. The IGS lists irradiation as producing red, deep pink, yellow, orange and parti-colours, and says it is undetectable and may fade with heating or prolonged bright light. It also warns against names such as Brazilian emerald for green tourmaline. A real tourmaline under a borrowed name is still mislabelled. Nothing on this site is offered for sale; the wanted list is the only commercial route.