Obsidian
Natural glassJewelryWiki Editorial·1 source·Reviewed 2026-08-04
Volcanic glass, not a mineral — it cooled too fast for crystals to form, which is why it has no crystal structure and breaks into the razor-sharp curved shards that made it a cutting tool for most of human history. Cheap, striking, and soft enough that a ring will scuff.
Properties
| Property | Value | Authority |
|---|---|---|
| Mohs hardness | 5 [1] | — |
| Specific gravity | 2.25–3.00 [1] | — |
| Chemical formula | No fixed formula. IGS gives a variable composition of roughly 66–72% SiO2 plus oxides of calcium, sodium and potassium — a glass is a composition range, not a compound. [1] | — |
| Crystal system | Amorphous — no crystal structure, which is what makes it a glass rather than a mineral. [1] | — |
| Suitability for daily wear | Poor for rings. At Mohs 5 it is softer than household dust and scratches easily; it also chips into sharp edges rather than rounding. [1] | — |
| Care cautions | Avoid knocks and ultrasonic cleaners. Wipe with a soft cloth. [1] | — |
Sources
- International Gem Society — gemstone articles — International Gem Society (IGS, gemstone information articles (gemsociety.org))