Onyx, Obsidian, and Black Tourmaline: What Sets Them Apart

By Terra Sigil · 2026-06-28 · Crystal Guides

Photo: James St. John, Wikimedia Commons — CC BY 2.0

Three stones sit in a palm: all black, all smooth, all sold in the same shop. A customer browsing a crystal retailer in 2014 put it plainly — she was interested in several of the gemstones but did not know where one ended and another began, and she had a follow-up question about aluminum in black tourmaline that the color alone could never answer. That question is actually three questions folded into one: origin, structure, and safety — and each stone answers differently.

Black is where the similarity stops. Onyx, obsidian, and black tourmaline are mineralogically unrelated. Understanding what each one actually is makes them easy to distinguish — and makes the aluminum question answerable.

Discussion statistics: 3 community records analyzed, 2 verbatim community quotes

What Is The Difference Between Onyx, Obsidian And Black Tourmaline?

Start with structure. Onyx is a variety of chalcedony — microcrystalline quartz — typically showing alternating bands of black and white, though sold and dyed as solid black in most markets. It has a true crystal structure, a Mohs hardness of about 6.5 to 7, and a waxy luster when polished.

Obsidian is volcanic glass. Lava cooled so rapidly that no crystal lattice had time to form, leaving an amorphous solid. It is technically not a mineral at all — mineralogy requires a repeating atomic structure, which obsidian lacks. It fractures conchoidally (in curved, shell-like breaks), produces very sharp edges, and reads as slightly lower on Mohs than quartz at around 5 to 5.5. The glassy luster is distinctly different from onyx's wax.

Black tourmaline — more precisely, the species called schorl — is a complex boron silicate mineral containing aluminum, iron, and several other elements depending on the specific chemistry. Its structure is quite different from both: it forms striated prismatic crystals, often with visible parallel grooves running the length of the stone. Mohs hardness is 7 to 7.5.

"I'm interested in several of the gemstones. I don't really know the difference between Onyx, Obsidian and Black Tourmaline. Also, I read one of your caution article about Black Tourmaline contains aluminum.....is this reference to wearing the jewelry or by placing somewhere?" — customer question, HealingCrystals, 2014

On the aluminum question: schorl's aluminum is part of its fixed mineral chemistry — it is not a surface treatment or additive. This is the same aluminum present in many common silicate minerals, including feldspars and garnets. External placement versus wearing is a distinction drawn by practice preference, not by the mineralogy itself.

What Is The Difference Between Black Obsidian And Apache Tears?

Apache Tears are obsidian — the same volcanic glass, not a separate mineral. The distinction is one of form and appearance. Apache Tears are small, rounded nodules that separated from a larger obsidian body and were smoothed and shaped by weathering over time. Their characteristic feature is translucency: a thin Apache Tear held up to a light source allows light through, appearing smoke-grey or reddish-brown rather than opaque black.

Standard obsidian in larger pieces is typically opaque. The translucency of Apache Tears comes from their small size and the way light interacts at the thinned edges of rounded nodules — the material is the same.

"I've just bought a piece of Apache Tears. I was looking for a larger piece of obsidian for scrying, I wondered what the difference was between the two. I didnt know Apache Tears was translucent till i read your detail about it ... amazing. Thanks for all the info on all the crystals its great!" — customer question, HealingCrystals, 2013

For scrying — the use the customer above was weighing — larger flat obsidian is the more practical choice. Apache Tears suit handled or pocket use, where their rounded shape and weight make them easy to hold.

What Is The Difference Between Jet and Obsidian?

Jet is the one black stone in common crystal commerce with a biological origin. It is fossilized wood — specifically, a form of lignite derived from ancient woody plant material compressed over geological time. It is organic in the chemical sense, the same category as amber or coral.

Obsidian is inorganic volcanic glass. The two are as different in origin as bone and basalt. Practical differences follow: jet is lighter than obsidian (lower density), may show a faint woodgrain texture in some pieces, and produces a brown streak when scraped on unglazed porcelain — obsidian gives a white streak. Jet is also softer (Mohs around 2.5 to 4) and warmer to the touch than glass.

The community comparison more often runs jet against onyx than against obsidian, because both appear in European and North American mourning jewelry traditions. Obsidian sits in a different historical lineage — volcanic and high-altitude cultures where the material was valued for toolmaking before entering spiritual use.

How the Four Compare at a Glance

What the Stones Add Up To

Onyx, obsidian, and black tourmaline share a color but differ completely in origin and structure: onyx is a banded form of chalcedony (microcrystalline quartz), obsidian is volcanic glass with no crystal lattice at all, and black tourmaline is a complex boron silicate mineral. Apache Tears are a rounded, translucent variety of obsidian — not a separate mineral — while jet is fossilized organic wood, making it the only one of these black stones with a biological origin. The fastest field test: hold the piece to a bright light. Apache Tears show translucency; true obsidian and onyx remain opaque; tourmaline reveals parallel striations; jet feels warmer and lighter than any of them.

FAQ

What Is The Difference Between Onyx, Obsidian And Black Tourmaline? Onyx is banded chalcedony (microcrystalline quartz) with a waxy luster and Mohs hardness of 6.5–7. Obsidian is volcanic glass with no crystal structure, a glassy luster, and Mohs around 5–5.5. Black tourmaline (schorl) is a complex boron silicate with visible striations and Mohs 7–7.5. All three appear black but are mineralogically unrelated.

What Is The Difference Between Black Obsidian And Apache Tears? Apache Tears are rounded obsidian nodules shaped by weathering — the same volcanic glass as obsidian. The key distinction is translucency: Apache Tears are small enough that a thin edge held to light passes through, appearing smoke-grey. Larger obsidian pieces remain opaque. For scrying, larger flat obsidian is more practical; Apache Tears suit handled or pocket use.

Discount Prices on Healing Crystals, Minerals & Tumbled Stones hey, can you tell me the difference between jet and obsidian? Jet is fossilized organic wood (a form of lignite) — lightweight, Mohs 2.5–4, warm to the touch, with a brown streak on unglazed porcelain. Obsidian is inorganic volcanic glass — denser, Mohs 5–5.5, cool and glassy, with a white streak and conchoidal fracture. They share a black color but have entirely different origins.