Igneous Rocks · common
Obsidian
Obsidian is a naturally occurring volcanic glass formed from rapidly cooled lava. Its sharp edges made it invaluable for ancient tools and weapons.
Also known as: volcanic glass, black glass, apache tears.
Obsidian properties at a glance
| Type | Igneous Rocks |
|---|---|
| Chemical formula | SiO2 (70-75%) |
| Mohs hardness | 5.5 |
| Crystal system | amorphous |
| Luster | vitreous |
| Streak | White |
| Cleavage | None |
| Fracture | Conchoidal |
| Specific gravity | 2.4 |
| Transparency | translucent |
| Common colors | Black, Brown, Green, Rainbow |
| Rarity | common |
Geology & background
Forms when volcanic lava cools rapidly with minimal crystal growth, creating natural volcanic glass.
One of the first materials used by humans for cutting tools, dating back to the Stone Age.
How to identify Obsidian
- Check whether the specimen's color and texture match typical Obsidian examples.
- Photograph a fresh surface in natural light and avoid shadows, glare, or wet surfaces.
- Use hardness, streak, luster, grain size, and locality together; no single trait is enough for every specimen.
Full Obsidian identification guide: checklist, home tests and look-alikes →
Obsidian vs similar stones
Not sure it isn't something else? Side-by-side comparisons with the stones most often confused with Obsidian.
Where Obsidian is found
Obsidian is reported from multiple localities or geological settings. Exact locality should be verified from specimen provenance, maps, or field notes.
How much is Obsidian worth?
| Entry-level specimen | $5 |
|---|---|
| Typical collector specimen | $20 |
| Premium specimen | $100+ |
Value depends on size, condition, color, crystal quality, locality, rarity, preparation, and provenance. Treat this as educational guidance, not an appraisal.
Common uses
- Jewelry
- Surgical scalpels
- Decorative objects
- Spiritual practices
Interesting facts
- Can be sharper than surgical steel scalpels
- Used by ancient peoples for weapons and tools
- Some obsidian contains tiny bubbles creating 'snowflake' patterns
Care & safety
Treat Obsidian as a collector specimen unless hardness, cleavage, and fracture are confirmed.
Avoid inhaling dust. Do not cut, grind, or polish unknown specimens without eye protection and a properly rated respirator.
Obsidian FAQ
What is Obsidian?
Obsidian is a naturally occurring volcanic glass formed from rapidly cooled lava. Its sharp edges made it invaluable for ancient tools and weapons.
How much is Obsidian worth?
Entry-level Obsidian specimens sell for around $5, a typical collector specimen for about $20, and premium pieces for $100 or more. Value depends on size, condition, color, crystal quality, locality, rarity, preparation, and provenance. Treat this as educational guidance, not an appraisal.
How hard is Obsidian?
Obsidian has a Mohs hardness of 5.5. It is about as hard as window glass: a knife barely marks it, while a steel file (Mohs 6.5) will.
Where is Obsidian found?
Notable sources of Obsidian include Mexico, USA, Japan, Iceland, and Italy. Forms when volcanic lava cools rapidly with minimal crystal growth, creating natural volcanic glass..
What is Obsidian used for?
Obsidian is used for jewelry, surgical scalpels, decorative objects, and spiritual practices.
