Black Tourmaline or Obsidian: How to Tell Them Apart
One glance is enough, and it costs nothing: black tourmaline runs with parallel striations along its length, obsidian never does. Here's what really sets these two stones apart, their properties, five checks you can do at home including a small static-electricity experiment, and what crystal healing credits each one with.
A glass and a crystal
Obsidian isn't a crystal. It's a natural volcanic glass: silica-rich lava that cooled before it could organise itself, leaving its atoms in disorder just as in a window pane. It's classed as a mineraloid. Its origin story is covered in detail in how obsidian is formed.
Black tourmaline, which mineralogists call schorl, is the opposite: a perfectly crystallised mineral, trigonal in system, belonging to the highly complex borosilicate family. It owes its black colour to a high iron content and grows in elongated prisms, in pegmatites and metamorphic rocks from Brazil, Madagascar, Namibia or Pakistan.
This difference in nature leads to the one thing worth remembering: a crystal grows along axes, and that growth leaves marks. On tourmaline, these are parallel grooves running the full length of the prism, deep, regular, impossible to mistake for anything else. A glass has no growth axis at all: obsidian is smooth, everywhere, always.
Obsidian and black tourmaline: the comparison table
| Criterion | Obsidian | Black tourmaline (schorl) |
|---|---|---|
| Nature | Volcanic glass, amorphous | Crystalline mineral, trigonal system |
| Composition | Silicate glass, over 70% SiO₂ | Complex iron-rich borosilicate |
| Hardness (Mohs) | 5 to 5.5 | 7 to 7.5 |
| Density | 2.35 to 2.60 | 3.02 to 3.26 |
| Refractive index | 1.48 to 1.51 | 1.62 to 1.65 |
| Birefringence | None (isotropic) | 0.014 to 0.024 |
| Surface | Smooth, deep vitreous lustre | Pronounced longitudinal striations |
| Fracture | Conchoidal, shell-like | Irregular, brittle |
| Rough form | Shards with no fixed shape | Elongated prisms, triangular cross-section |
| Electricity | None | Pyroelectric and piezoelectric |
| Origin | Mexico, USA, Iceland, Italy | Brazil, Madagascar, Namibia, Pakistan |
In short, three lines do all the work. The striations are visible to the naked eye. The density (≈ 2.45 versus ≈ 3.15) is obvious in the hand. And electricity is a property obsidian simply doesn't have, put to use below.
Five tests you can do at home
From most to least reliable, and all non-destructive except the last one, which I'd steer you away from.
Look for the striations
The decisive test, free and instant. Tilt the stone toward a window: if parallel grooves appear running in one direction, it's tourmaline. They stay visible even on tumbled stones or beads, where they show up as fine, regular dark lines. Obsidian has nothing to show: just a smooth surface.
Weigh it in hand
A bracelet of 22 beads at 8mm weighs around 14.5g in obsidian versus 18.5g in tourmaline, nearly 30% more. It's less dramatic than with some very dense stones, but perfectly noticeable with one bracelet in each hand, and unmistakable on a kitchen scale.
The static electricity test
The most fun, and the least well known. Tourmaline is pyroelectric: when warmed, it develops an electric charge and attracts dust. Eighteenth-century Dutch traders called it aschentrekker, "ash puller", because it drew ash from a pipe. Rub the stone briskly in a piece of wool, then bring it near tiny bits of paper: tourmaline attracts them, obsidian doesn't. Never heat it with a flame, the warmth of your hand or the sun is enough, and thermal shock damages the stones.
Check the fracture and lustre
On a raw shard, obsidian shows a conchoidal fracture, curved, shell-like surfaces with sharp edges, and a deep, almost liquid vitreous lustre. Tourmaline breaks irregularly and looks more matte, more "mineral" in character.
Scratch it, best avoided
A steel point (hardness ≈ 5.5) scratches obsidian but not tourmaline (7 to 7.5). The test works, and it permanently damages the piece. The four tests above are more than enough; if you really insist, work on a hidden spot.
Worth noting, none of these tests replace a proper gemmological examination. For a valuable piece, or a dispute with a seller, only an independent lab can settle it: tourmaline's birefringence, absent in obsidian, is measured with a refractometer in minutes.
What crystal healing credits each one with
Both are sold as "protection stones", and that's exactly where the confusion creeps in. In tradition, though, they're credited with different roles.
Black tourmaline
Described as a shield facing outward. It's credited with a defensive role: deflecting, filtering, holding a line. It's the stone recommended for heavy environments.
Black obsidian
Described as a mirror facing inward. It's credited with less defence and more clarity: it reflects, confronts, surfaces what's beneath. It protects through insight rather than deflection.
I find this distinction genuinely useful: it explains why some people find obsidian too blunt where tourmaline suits them better. The topic is covered in obsidian, protection and grounding, and if obsidian feels too intense for you, dangers and precautions addresses it directly.
People often ask me which one is "more powerful". It's not a question I can honestly answer, these properties are matters of belief, not measurement. What I can say is that plenty of people wear both together, and there's nothing inconsistent about that.
Obsidian also pairs very well with other dark stones: see my guide to crystal pairings, including the tiger's eye duo.
The other black stones people confuse it with
Tourmaline isn't the only contender. Three other black materials circulate under loosely applied labels:
- Black spinel, a very dense (≈ 3.60) and very hard (7.5 to 8) cubic mineral. Almost always faceted with sharp, sparkling cuts, which gives it away immediately: neither obsidian nor tourmaline is worked this way;
- Black onyx, a chalcedony, hardness 6.5 to 7, whose uniform commercial black is almost always achieved through dyeing. Matte, perfectly uniform in appearance, without obsidian's glassy quality or tourmaline's striations;
- Manufactured black glass, the only genuine problem in this list. Too perfect, no inclusions, often translucent at the edge and sometimes marked with a mould line. It warms up very quickly in the hand. It's what's behind those "blue obsidians" in impossible colours.
Sorting them is quick: striated → tourmaline. Faceted and sparkling → spinel. Matte and perfectly uniform → dyed onyx. Too perfect and too light → glass. Obsidian, meanwhile, almost always keeps a small imperfection, a bubble, a haze, a shift in tone within the black. Inflated prices and fanciful names are covered in obsidian price and value.
Which one should you choose?
On technical grounds, worth saying upfront: tourmaline is tougher. At 7 to 7.5 on the Mohs scale against 5 to 5.5, it takes everyday knocks far better. For a ring worn daily, that's a real argument.
What obsidian has going for it is a different kind of appeal. Its black isn't matte but deep, almost liquid depending on the light, the lustre of glass, which tourmaline's more mineral finish simply doesn't give. It polishes to a level few stones reach, which is exactly why it was made into mirrors for centuries. And its material tells a story: cooled lava, a geological accident.
I don't work with tourmaline, and it isn't on principle: obsidian is simply enough for me. That black that shifts with the light, matte one moment and almost liquid the next, I've never managed to tire of it. Tourmaline is a beautiful stone; it just isn't mine.
In practice: tourmaline if you're after toughness and a matte black; obsidian if you're after depth and a story. If you're unsure about sizing, the jewellery size guide will help; and for the full picture, the complete obsidian guide covers origin, varieties and care.
✦ The deep black of volcanic glass
My handmade obsidian pieces
Loading creations…
Precautions & care
The hardness gap has an immediate consequence: don't store your two stones together. Tourmaline, at 7-7.5, scratches obsidian effortlessly. Each piece deserves its own fabric pouch or compartment.
For obsidian: a soft microfibre cloth, a brief rinse in lukewarm water if needed, never salt, abrasive products, ultrasonic cleaners or steam. Take your jewellery off before showering, exercising or sleeping, on a bracelet strung on elastic cord, the cord is the first thing to wear out. It's all covered in cleansing and charging obsidian.
Good to know, the gemmological figures quoted here (hardness, density, refractive index, pyroelectricity) are measurable data. The properties credited to stones, on the other hand, come from spiritual traditions and crystal healing, a wellbeing practice based on belief. They are not a medical claim, do not treat any condition, and never replace advice from a health professional.
Frequently asked questions
How do you tell black tourmaline from obsidian?
What is schorl?
Is black tourmaline really electric?
Which one is harder?
Can you wear black tourmaline and obsidian together?
Which one is more expensive?
How can you recognise genuine obsidian?
Your obsidian, handmade
Bracelets, necklaces, pendants and rings in natural obsidian, handcrafted in France, every variety sold under its true name.