Black obsidian and jet displayed side by side

Obsidian vs Jet: How to Tell the Two Black Stones Apart

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Obsidian and jet are both black, both polish well, and both turn up in beads, carvings and pendants. They are different materials. Obsidian is natural volcanic glass. Jet is fossilized wood, a dense form of lignite. Obsidian is harder, heavier and cool in the hand. Jet is softer, lighter and warm.

This guide compares the two on origin, appearance, physical properties and identification. It also covers common imitations, the limits of home tests, and what the two stones mean in cultural history.

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TL;DR

  • Obsidian is volcanic glass (Mohs about 5 to 5.5). Jet is fossil wood, an organic rock (Mohs about 2.5 to 4).
  • Jet feels warm and light. Obsidian feels cold and heavier for its size.
  • Jet leaves a brown streak on unglazed porcelain. Obsidian breaks with curved, glassy fracture surfaces.
  • Black glass, plastics and hard rubber are common jet imitations. Small polished pieces can look identical, so a seller’s description and provenance matter.
  • Black obsidian is widely available as raw chunks, palm stones, eggs and carvings. Jet is a rarer, more specialized material.

Table of Contents

The short comparison

Feature Obsidian Jet
What it is Natural volcanic glass Fossil wood, a form of lignite
Origin Silica-rich lava that cooled very fast Wood buried in sediment and coalified
Mohs hardness About 5 to 5.5 About 2.5 to 4
Specific gravity About 2.35 to 2.6 About 1.3 to 1.4
Touch Cold Warm
Luster Glassy Velvety to vitreous when polished
Fracture Conchoidal (curved, shell-like) Not glassy; carves and cuts easily
Streak Not brown Brown

The hardness, density, touch, luster and streak figures follow the Rocksday jet and obsidian comparison. The sections below tie each row to a second source where one exists.

What each stone is

Obsidian: glass made by volcanoes

Obsidian forms when silica-rich lava cools so quickly that crystals have no time to grow. The result is an amorphous solid, which is why it is classed as a natural glass and not as a crystal in the strict mineral sense. The International Gem Society describes obsidian as natural glass formed by volcanism, with an amorphous structure and conchoidal fracture.

That origin has a practical side for collectors. Obsidian occurs wherever suitable lava flows exist, including Canada. The Geological Survey of Canada describes the Armadillo Formation in British Columbia, a Miocene unit that includes comenditic rhyolite flows, some with a vitreous, flow-banded obsidian base. This is a geological record, not a place to collect. Digging on Crown land, in parks and on private property is regulated, so check the rules before picking up stone in the field.

Obsidian is not always plain black. Cooling conditions, inclusions and tiny gas bubbles produce snowflake, mahogany, rainbow, sheen and golden varieties. The Legacy guide to obsidian varieties and cooling clues explains how those differences form and how to read them.

Jet: fossil wood

Jet is an organic rock. Woody material is buried in sediment and slowly coalified in isolation, which gives a dense, black, coal-like material. Geology.com describes jet as an organic rock similar to coal and one of a small group of organic gemstones. The same page notes that jet gave English the phrase “jet black”, meaning as black as possible. So “jet black” is a colour word. It does not name a mineral, and it does not mean the stone is obsidian or black onyx.

Jet has a long history in jewelry. The Whitby Museum notes that jet is easily carved and polished, and that it was used for ornaments and for Victorian mourning pieces. Whitby in northern England is the best-known source, which is why “Whitby jet” is a common trade phrase.

Appearance: how they look side by side

Both stones are black, so colour alone settles nothing. Surface character does better.

Obsidian

  • Reflective, glassy surface, even when only lightly polished.
  • Thin edges and thin flakes can let light through. Held against a strong light, they may show a grey or smoky tone.
  • Raw pieces show smooth, curved fracture surfaces with ripple-like lines.
  • Some pieces show sheen, banding, snowflake patterns or a rainbow play of colour.

Jet

  • A softer, deeper black. Polished jet is often described as velvety, and it can take a glassy polish.
  • A waxy or dull luster before final polishing. The International Gem Society lists jet’s luster as dull and waxy and notes that it takes a vitreous polish.
  • Rarely shows see-through edges. It is opaque.
  • Sometimes shows faint wood grain or fine cracks in the surface.

A finished obsidian piece tends to look like black glass. A finished jet piece tends to look like dense, deep black with a softer sheen. Under poor light, this difference is hard to see.

Physical properties that separate them

Hardness

Obsidian sits around 5 to 5.5 on the Mohs scale. Jet is much softer, around 2.5 to 4, according to Rocksday. In practice, jet scratches and wears more easily. A bracelet of jet beads will show wear sooner than one of obsidian beads. Jet is also easy to carve, which is why it was a favoured material for detailed jewelry. Obsidian takes fine work too, but it is brittle and chips along curved fractures.

Weight

Jet is light. Its specific gravity is about 1.3 to 1.4, against about 2.35 to 2.6 for obsidian. Two pieces the same size will feel clearly different. The obsidian piece feels like stone. The jet piece feels closer to a dense plastic or hard wood. This is one of the most useful checks for larger pieces such as eggs, spheres and carvings. It is less useful for tiny beads.

Temperature

Obsidian feels cold when first picked up. Jet feels warm, because it is a poor conductor of heat, as the Whitby Museum explains. Glass and stone draw heat from the hand faster, so they feel cooler. Try this with the piece at room temperature, not freshly out of a cold car or window display.

Fracture and wear

Obsidian is known for conchoidal fracture: a break leaves smooth, curved, shell-like surfaces, like broken bottle glass. This is why obsidian was used for sharp tools and blades. Jet does not behave like glass. It is a carbon-rich organic material that carves, cuts and abrades.

Do not break a piece to test it. Look at existing chips or edges on the underside or base. Fresh damage lowers the value of any specimen.

Streak

Rubbing a piece on an unglazed porcelain tile leaves a streak. The Whitby Museum states that jet leaves a brown streak. Use an inconspicuous spot, such as the base, because a streak test can leave a mark. Test only pieces you own, and never on a polished face.

How to check a piece you own

None of these checks is lab proof. Together they give a sound first answer.

  1. Weigh it and compare size to heft. A piece that feels light for its size points to jet or an imitation. A piece that feels like stone points to obsidian or another mineral.
  2. Touch it. Cold at first, then slow to warm, suggests glass or stone. Warm at once suggests jet or plastic.
  3. Check the edges. Thin edges that glow grey against a bright light suggest obsidian. Opaque edges suggest jet or another opaque black material.
  4. Look for conchoidal chips. Curved, shell-like chips on a worn edge suggest glass.
  5. Run a streak test on the base. A brown streak points to jet. Note that ebonite and vulcanite also leave a brown streak.
  6. Compare to a known reference. A labelled piece of black obsidian from a reputable source is a useful benchmark.

A few tests apply to either stone. Do not use a hot needle on jewelry you plan to keep, and do not scratch visible surfaces with a knife. Both leave damage, and a hot needle can ruin organic material.

Imitations and why they matter

Jet has been copied for well over a century. The Whitby Museum lists vulcanite, ebonite, bakelite and black glass as common jet imitations. Most do not leave a brown streak. Ebonite and vulcanite do, so a brown streak alone does not prove a piece is jet.

Black glass is a special case. A piece of obsidian is natural glass, while black glass sold as jet is manufactured. They can look similar, and a weight and temperature check will not separate natural obsidian from man-made glass. For that, provenance and a clear seller description matter more than a home test.

The limits of home identification

Small, finished objects are the hardest. A study of archaeological jet-like artifacts, published in the journal Archaeometry, recommends combining XRF and X-radiography, and notes that XRF may not clearly classify every sample. The study also notes that jet was one of several black materials used for jewelry, and that small worked objects can be visually indistinguishable.

The Gemological Institute of America makes a similar point in a paper on identifying black opaque gem materials. Basic gemological tests may not identify black opaque materials without doubt. Advanced methods such as X-ray diffraction and EDXRF are often needed, and they may not be conclusive either.

What this means for a buyer:

  • Treat home tests as a screen, not a certificate.
  • For a valuable or antique piece, ask a gemological laboratory or a museum mineralogy department about testing.
  • Buy from sellers who state the material, the variety and, where known, the locality.

Other black stones that get mixed up

Searches for these two stones often lead to a third or fourth. A quick map:

  • Black tourmaline (schorl): a true crystal, often with vertical striations. It is opaque and not glassy in the way obsidian is.
  • Black onyx: a banded form of chalcedony, usually dyed black when sold as jewelry. It is harder than obsidian and takes a high polish.
  • Tektite: natural glass of impact origin, often confused with obsidian. The Legacy guide on telling tektite from obsidian covers three lab tests.
  • Apache tears: small, rounded obsidian nodules, translucent when held to light.

“Jet black” is also a common colour label on beads and dyed stones. A listing that says “jet black” may describe colour only. Read for the material name.

Cultural meaning: what is documented

Both stones carry long human histories. This section covers documented use, not claims about effects on the body.

Obsidian. The San Diego Archaeological Society notes that the Aztecs associated polished obsidian mirrors with the god Tezcatlipoca and used them for divination, regarding them as portals to ancestors and gods (Obsidian: The Smoking Mirror). In North America, the U.S. National Park Service writes that the Hopewell people likely viewed obsidian as strongly connected to the spiritual world. Ceremonial spearpoints were likely displayed or used in religious events, and sometimes ritually broken (Hopewell Culture Obsidian). Today, the same page notes, obsidian is used in jewelry and decorative elements.

For readers who use black obsidian in meditation or grounding practice, the Legacy article on black obsidian meaning and origins sets out the traditional associations and the stone’s origins. These are cultural and personal practices, and they are separate from the mineral facts above.

Jet. Jet’s best-documented role is in mourning jewelry. The Whitby Museum links it to Victorian mourning pieces. That is a historical fashion, and it is a different thing from the spiritual use of obsidian.

Which one suits which buyer

Collectors of raw specimens. Obsidian is the more practical choice. It is durable enough to handle, it forms in distinct varieties, and a raw piece shows its volcanic origin through fracture and flow banding. A raw chunk shows exactly how the material formed.

Raw Black Obsidian Chunks

Carving and display buyers. Obsidian carvings hold sharp detail and a mirror polish. Jet is softer, so carved edges and fine detail can wear faster. Check each listing for the material and the finish.

Jewelry wearers. Obsidian beads and bracelets are lighter on cost and tougher in daily wear than jet. Jet is lighter in weight, which suits long necklaces and larger pendants, but it needs gentler care. Store it apart from harder stones that can scratch it.

Heirloom or antique pieces. Pieces sold as old jet or Victorian jewelry deserve separate testing. Keep them somewhere safe and dry; a guide to jewelry and heirloom storage covers the options.

For a wider view of how collectors weigh materials against each other, the Legacy piece on minerals versus gemstones explains why many buyers prefer natural, uncut specimens. Buyers who also collect carved stone objects can read a collector’s overview of sculpture stones for how different stones differ in carving.

Care for black stones

Obsidian and jet need different handling.

  • Obsidian: keep it away from hard knocks, since it chips along fracture lines. Wipe it with a soft, damp cloth. Store pieces separately or wrapped so they do not rub against harder minerals.
  • Jet: keep it away from heat, solvents and harsh cleaners, since it is an organic material. Wipe it with a soft dry or barely damp cloth. Store it by itself, away from harder stones.

Pieces in a display case should sit away from direct sun and radiators. Heat can crack both stones.

Shopping for obsidian at Legacy

Legacy Crystals and Minerals sells obsidian in several forms, shipped to Canadian buyers. The range covers raw specimens, polished stones, carvings and jewelry:

Prices are shown on each product page. Browse the full raw minerals and crystals collection or the museum quality minerals range for pieces with a stronger collector focus.

Raw Black Obsidian Chunks

Each listing names the material. That is the first step in any identification: a clear name, a clear form, a clear photograph.

Buying checklist

  1. The listing names the material (obsidian, jet, black glass), not only a colour.
  2. The variety is stated: black, snowflake, mahogany, golden, sheen.
  3. Weight and size are given, so the heft can be checked.
  4. Photographs show edges, base and any chips.
  5. The seller explains the source of the piece, where known.
  6. The return terms are clear.

FAQ

Is jet the same as obsidian?

No. Jet is fossil wood, a form of lignite, and obsidian is volcanic glass. They differ in hardness, weight and feel. Obsidian is harder and heavier and feels cold. Jet is softer and lighter and feels warm.

How can I tell obsidian from jet at home?

Start with weight, touch and edges. Obsidian feels heavy and cold and may show grey through thin edges. Jet feels light and warm, and it leaves a brown streak on unglazed porcelain. Imitations such as ebonite also leave a brown streak, so these checks narrow the answer without confirming it.

Is black obsidian or jet the same as black onyx?

No. Black onyx is a banded form of chalcedony, usually dyed black for jewelry. It is a harder, quartz-family stone. “Jet black” is a colour description that comes from the name of jet, and it does not name a stone.

How can I tell if black obsidian is real or fake?

Natural obsidian shows conchoidal fracture, a cool touch and a glassy luster. Manufactured black glass can look identical, so home tests cannot always separate the two. Buy from a seller who names the material and its source. For a high-value piece, a gemological laboratory can run advanced tests.

Sources

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