Real vs Fake Obsidian: 6 Tests That Work and 3 That Don't

Search for a black obsidian necklace and you will find pieces at $8 and pieces at $260. Both are described as genuine natural obsidian. In a photograph, they look almost identical.

That gap is why this article exists.

I have been cutting and setting natural stone at our workshop in Tbilisi for seven years, and obsidian is one of the materials I work with most often. Cutting a stone yourself teaches you things a description never will. That includes which of the tests repeated endlessly online actually tell you something, and which prove nothing at all.

This guide covers both.

What obsidian actually is

Understanding the material is what makes the tests make sense.

Obsidian is not a mineral. It is a volcanic glass, rock formed when silica-rich lava cools so quickly that its atoms never arrange into a crystal structure. Its composition sits close to rhyolite and granite.

Three things follow from that, and every reliable test comes out of them:

1. It is about as hard as window glass, not harder.
2. It breaks in curved surfaces with edges sharp enough that obsidian blades were used through the Stone Age and still appear in some surgical scalpels.
3. It is glass, which is exactly why separating it from manufactured glass is the hard part.

Obsidian forms wherever there has been recent volcanic activity: Iceland, Japan, Mexico, Italy, Greece, Kenya, Russia, the western United States and Armenia among them.

Black is the most common colour. Brown, tan and green occur naturally; blue, red, orange and yellow are rare. Those colours come from trace elements and inclusions, not from treatment.

Three named varieties you will meet while shopping:

• Snowflake obsidian. Grey or white patches of cristobalite that crystallised inside the glass over time
• Mahogany obsidian. Black and reddish-brown swirled together
• Rainbow, golden and silver sheen obsidian. Iridescence caused by microscopic inclusions or gas layers aligned inside the stone

What "fake obsidian" usually turns out to be

"Fake" covers four different things, and they are not equally easy to catch:

1. Manufactured black glass. The most common substitute and the hardest to identify, because obsidian is glass.
2. Plastic or resin. The cheapest, and caught by almost every test below.
3. Dyed or treated stone. Black-dyed agate, onyx or quartzite. Harder than obsidian, which is what gives it away.
4. Reconstituted material. Crushed stone bound in resin and pressed into shape.

Knowing which one you are looking at changes which test is worth doing.

The 6 tests that work

All of these can be done at home, with no equipment beyond a lamp.

1. Hold a thin edge against a strong light

Obsidian is documented as transparent to opaque, not uniformly opaque. Hold the piece so a lamp shines through its thinnest part: the rim of a cabochon, or the edge beside a drill hole. Most of the black obsidian we cut lets light through.

In our workshop that transmitted light is usually a warm brown or olive tone. Dense black plastic and heavily pigmented glass tend to stay flat and dead black.

Catches: plastic, opaque imitations · Misses: good black glass

2. The warmth test

Glass and stone both draw heat away from your skin. Pick the piece up and hold it in a closed hand.

• Obsidian feels cool on contact and warms slowly, over roughly half a minute
• Plastic or resin reaches skin temperature almost immediately

This one test eliminates the majority of very cheap fakes.

Catches: plastic, resin · Misses: glass, dyed stone

3. Look at a broken or unpolished edge

Obsidian breaks with a conchoidal fracture: smooth curved surfaces, like the inside of a shell, meeting at genuinely sharp edges.

Dyed agate and quartzite break granular and dull. Resin chips soft and pale. Moulded plastic shows a seam.

Do not create a break to test this. Look at edges that already exist: the back of a cabochon, the inside of a drill hole, an unpolished side.

Catches: dyed stone, resin, moulded plastic · Misses: manufactured glass

4. Test hardness the right way, and know the trap

Obsidian sits at 5 to 5.5 on the Mohs scale. That number is more useful in reverse than most articles admit.

• A fingernail (2.5) or a copper coin (3.5) leaves no mark on obsidian. If either scratches your piece, it is soft material: resin, plastic or a coating.
• A stone that easily and deeply scratches glass is probably harder than obsidian. Quartz sits at 7; agate and onyx are close to it. That points to dyed stone.

Test on the least visible surface, the back or the area beside the drill hole. Never on the display face.

Catches: resin, plastic, dyed quartz and agate · Misses: glass of similar hardness

5. Read the pattern for irregularity

For snowflake, mahogany and sheen varieties, the pattern is the evidence.

Natural cristobalite patches in snowflake obsidian vary in size, spacing and density. Some cluster, some stand alone, and their edges are soft and irregular. Natural mahogany banding flows and swirls unevenly. It was liquid once, and it looks it.

Printed or moulded imitations repeat. Look for identical shapes appearing twice, evenly spaced dots, or a pattern that stops exactly at the stone's edge instead of running off it.

Catches: printed and moulded imitations · Misses: plain black glass

6. Weigh it in your hand

Obsidian's specific gravity is typically 2.33-2.42. Plastic and resin sit near 1.0-1.4, roughly half as dense.

That difference is large enough to feel. A piece that seems suspiciously light for its size is almost certainly not stone.

What this test will not do is separate obsidian from other stones. Quartz and agate are only slightly denser, and no hand can measure a ten-percent difference.

Catches: plastic, resin · Misses: glass, dyed stone

The 3 tests that prove nothing

These circulate widely. Following them will make you reject good stones.

Myth 1: "Bubbles inside mean it's fake"

This is the most damaging one, because it is exactly backwards.

Gas bubbles are a normal feature of natural obsidian. They are degassing cavities, trapped and frozen while the lava cooled too fast to release them.

In 2025, GIA's Gems & Gemology documented an unusually vesicular obsidian from Arteni Mountain in Armenia's Aragatsotn region, a few hundred kilometres from our workshop. In that material the gas cavities reached more than two inches in length, separated by extremely thin, sharp walls.

So bubbles alone tell you nothing. What is worth noticing is their character: cavities in natural obsidian vary in size and often align in one direction, following the flow of the lava. Bubbles that are perfectly spherical, uniformly sized and evenly scattered through an otherwise flawless piece are the ones worth questioning.

Myth 2: "Real obsidian scratches glass"

Obsidian is 5 to 5.5 on the Mohs scale. Ordinary window glass is roughly the same. One will not reliably scratch the other, and pressing hard enough to force a mark damages your stone for no information.

As covered in test 4, a stone that cuts glass easily is evidence against obsidian, not for it.

Myth 3: "Real obsidian is flawless and perfectly black"

The opposite is closer to the truth. Natural obsidian commonly contains gas bubbles, mineral inclusions, faint flow lines, and lets light through at its thinnest edges.

A piece that is absolutely uniform, absolutely opaque and absolutely free of internal features is more likely to be moulded glass than fine obsidian.

What home tests cannot do

Being honest about the limit matters more than adding a seventh test.

No test in this article separates natural obsidian from well-made manufactured black glass with certainty. They are the same class of material, and obsidian's refractive index of 1.48-1.51 sits in the same range as common glass. The distinction is made in a laboratory, by measuring refractive index and specific gravity precisely and examining inclusions under magnification.

What the six tests above do reliably catch is plastic, resin, dyed stone and moulded imitation, which together account for most of what is actually sold as fake obsidian.

For the remaining case, the answer is not a better home test. It is a better seller.

The piece that taught me this

I learned this the expensive way.

Years ago, when I was still learning to cut, I bought a stone I was certain was obsidian. It was small enough to close my hand around. It looked right, and it felt right in the hand. It was also small and thick, with no thin edge anywhere on it, so the one test that might have caught it was the one test I could not perform.

I found out on the wheel. Cutting opens a stone, and what is inside cannot pretend to be something else. It was not obsidian.

What stayed with me was not the money. It was realising what I would have needed that day. Not a better eye, and not a seventh test. I would have needed the person selling it to tell me the truth about what it was.

Four questions worth asking a seller

1. Where was the stone sourced? A specific region is a better answer than "natural."
2. Is it treated, dyed or stabilised in any way? Anyone who works with the material will answer this plainly. With some stones the honest answer is yes, and it does not make the stone any less natural. I explain one of those cases in the article on aquamarine and heat treatment.
3. Can I see the back and the drill hole? The unpolished surfaces carry the evidence.
4. Who cut and finished it? A workshop that cuts its own stone can tell you. A reseller usually cannot.

When doubt does not go away

A customer once came to the workshop convinced the stone they owned was not real.

I showed them everything the workshop can show. The unpolished back. The inside of the drill hole. Light through the thinnest edge. How the material behaves under a blade. They still did not believe me, and they could not name what had made them doubt it in the first place.

So we sent it to a laboratory. The report came back: natural.

I do not tell this to say they were wrong to ask. They were right to ask, and right not to settle for my word alone. Anyone who is confident in their material has no reason to be afraid of a laboratory report. If you have real doubt about a piece that matters to you, a gemmological laboratory will settle it, and an honest seller will tell you the same.

How we work with obsidian at Akra

We cut and finish every obsidian piece by hand in our workshop in Tbilisi and set it in 925 sterling silver. Working the stone ourselves means we see the inside of every piece before it becomes jewellery: the flow lines, the bubbles, the light that passes through a thin edge.

Our obsidian comes from Armenia. Finding the right material took a long search. I knew what I wanted and most of what I was shown was not it. The supplier I ended up working with is someone I know personally, and in all that time he has never described a stone to me as something it was not.

The stone in each product photograph is the stone described on that page, photographed here in the workshop. It is not a stock image or a catalogue substitute. Where a piece carries a visible inclusion or an unusual edge, that is in the photograph too. Natural material is not uniform, and we would rather show you what it is than an idealised version of it.

One piece opened on the wheel with a colour I had not expected to find in it. I set it anyway, because everything about the stone said the colour had happened in the lava. A material that breaks conchoidally does not forgive a slip the way a harder, tougher stone does, and obsidian has broken on me, mostly in the early years while I was still learning it. That is a large part of why every piece here is cut slowly, and by hand.

See the raw black obsidian pendant we cut and set by hand →

Quick answers

Is black obsidian rare?

No. Obsidian is common wherever there has been recent volcanic activity. Its value in jewellery comes from the quality of the cut and finish, not from scarcity.

Does obsidian scratch easily?

It sits at 5 to 5.5 on the Mohs scale, softer than quartz. It will scratch against harder stones, so store obsidian pieces separately rather than loose with other jewellery.

Is snowflake obsidian real obsidian?

Yes. The pale patches are cristobalite, a mineral that crystallised inside the volcanic glass over time.

Why do some obsidian pieces show brown at the edges?

Because obsidian ranges from transparent to opaque. Held to a strong light, most black obsidian lets some light through at its thinnest points. It is a sign of natural material, not a flaw.