Obsidian: What It Is, How It Breaks, and How It Is Used

What it is

Obsidian isn't a mineral. It's glass, and the difference is bigger than it sounds.

When rock cools slowly, its atoms get time to line up in repeating patterns. That's what a mineral is, and it's also why you can identify most stones by breaking them. They split along the pattern. Obsidian never got that chance. The lava cooled too fast, the atoms froze wherever they happened to be, and what's left is a solid with no pattern inside it at all.

Which means no grain. Nothing to follow, no direction it prefers. You can't look at a piece of obsidian and predict what it will do when it's struck.

How it breaks

Break it and you get what geologists call a conchoidal fracture: a smooth curved surface that ripples outward from wherever the impact landed, like a wave with the water taken out. The edges of that break come out thinner than a blade can be manufactured.

This is why obsidian mattered so much before metal existed. It's also why no two pieces are alike. A stone with grain can be split along that grain, over and over, on purpose. Obsidian can't. Every break runs along the internal stresses of that particular piece of cooled lava, and no two pieces cooled the same way.

We finish it by hand and by eye for the same reason. There's no jig that will hold it, no template, no machine setting that produces the same result twice.

Where it turns up

Obsidian appears independently in places that had no contact with each other, and each one found a different use for it.

Mesoamerica

Polished into mirrors. The Aztecs used them for looking rather than for ornament, and getting volcanic glass to a true reflective surface is slow work.

Egypt

Ground and used around the eye. Same material property, that smooth fracture, aimed somewhere else entirely.

North America

Knapped into blades and points. Obsidian from one flow carries a chemical signature that differs from the next flow over, which is how archaeologists reconstruct trade routes that left no other trace.

The plateau

Carried, not displayed. On the Tibetan plateau obsidian sits closer to the body than to the eye, worn against the skin or kept in a pocket or pouch. It isn't a decorative material in that setting. It's a thing you keep on you.

Choosing one

Start with the surface. A good piece has a continuous, faintly waxy sheen. Dull patches usually mean someone abraded the surface instead of polishing it.

Then look for the flow. Plenty of pieces show faint banding, or a few bubbles trapped from the lava. Those aren't defects. They're the cooling, preserved.

Black isn't always black. Obsidian runs from true black to a smoky brown, and some pieces hold needle-like inclusions that catch light when you tilt them.

Last thing, and it's a real choice: polished or matte. Polished obsidian reflects the room and shows every fingerprint. Matte obsidian is quieter and holds its own colour. Same stone either way.

Care

Obsidian is hard but not tough. It scratches less easily than it chips, so keep it clear of hard edges and of other stones rattling around in a bag. Water and mild soap are fine. Solvents aren't. Over years a matte finish will slowly brighten where it touches skin. You can leave that alone, or bring it back with a soft cloth and a very fine abrasive.

What it pairs with

Obsidian is the darkest thing we work with, which makes it useful as a counterweight. Silver reads cold against it. Brass reads warm. A five-colour woven cord gives it the one thing it can't supply on its own.

Questions we get

Is obsidian a crystal?

No. It's glass. Crystals have repeating internal structures, and obsidian cooled before any could form. That's why people call it volcanic glass.

Will it chip?

Edges can. It fractures rather than bends, so a thin edge is far more exposed than a rounded one.

Is it heavy?

About the same as quartz of the same size, and much lighter than any metal. A stone 20 mm across weighs a few grams.

Does it stay black?

Yes. Obsidian doesn't fade. A matte surface brightens slowly where it's handled, and it can be brought back.