Obsidian
What is Obsidian?
Obsidian is a naturally occurring volcanic glass formed as an extrusive igneous rock. It is produced when felsic lava extruded from a volcano cools rapidly with minimal crystal growth. Obsidian is an amorphous material, meaning it lacks a crystalline structure. It is often found with a glassy texture and can be black, brown, or green in color, depending on the impurities present.
Optical Properties
- Refractive Index
- 1.44 - 1.51
- Birefringence
- None
- Pleochroism
- None
- Optical Character
- Isotropic
- Dispersion
- 0.010
Market Value Factors
Pricing varies for every rock and mineral, so use these universal factors to gauge Obsidian before comparing listings or appraisals.
Size & Weight
Larger, intact specimens usually command higher prices.
Rarity & Demand
Scarce material or popular varieties sell at a premium.
Condition & Finish
Chips, repairs, and heavy wear lower value; clean prep helps.
Treatment & Provenance
Untreated specimens with documented locality are prized.
Where to Find Obsidian
RockHoundR, the free-to-download rockhounding map from the Ruby Glint team, shows where collectors find obsidian in the US, with land-access notes for BLM land and national forests. Collecting is banned in national parks.
See where to find obsidianAlways check the local rules and get the landowner's permission before you collect.
More Images
Quick Facts
Physical Properties
- Color
- Black, brown, green, iridescent
- Hardness (Mohs)
- 5 - 5.5
- Rock tumbling
- With care
- Density
- 2.35 - 2.6 g/cm³
- Streak
- White to gray
Chemical Properties
- Chemical Formula
- SiO2
- Elements
- Silicon, oxygen, aluminum, iron, magnesium, calcium, sodium, potassium
Also Known As
Identify Obsidian Instantly
- Snap a photo, get instant results
- 6,700+ rocks, minerals & crystals
- Discover collecting spots near you
Obsidian FAQs
How do I identify Obsidian?
Obsidian can be identified by its hardness of 5 - 5.5 on the Mohs scale, Black color. Look for these key characteristics when examining specimens.
What color is Obsidian?
Obsidian typically appears in Black, brown, green, iridescent. Color can vary depending on impurities and formation conditions.
How hard is Obsidian?
Obsidian has a hardness of 5 - 5.5 on the Mohs scale. This gives it moderate hardness.