Gemstone profile and identification guide
Obsidian
Obsidian is a natural volcanic glass formed by rapid cooling of silica-rich lava.
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Overview
Obsidian is a natural volcanic glass formed by rapid cooling of silica-rich lava.
Did you know? Obsidian was a major prehistoric cutting material before widespread metal tool use.
Use this profile as a collector reference and educational guide for quick on-page comparison, then validate with the interactive identification system.
Identification
Name: Obsidian
Scientific classification: Mineraloid (Volcanic Glass)
Hardness: 5.5 Mohs
Transparency: opaque
Lustre: vitreous
Crystal system: Amorphous
Primary colour: Black
Secondary colour: Brown
Colour family: Blacks
Identified by glassy lustre, conchoidal fracture, amorphous structure, and lack of cleavage.
Verification Status
Status: verified-core-fields
Reference priority: GIA, Gem-A, Mindat, International Gem Society
Core identity, locality, and physical-property fields reviewed against standard gemological references.
Values are given as practical gemological ranges where appropriate.
Physical Properties
Hardness category: medium
Hardness value: 5.5 Mohs
Chemical composition: Natural silica-rich volcanic glass
Crystal system: Amorphous
Common locations: Mexico, United States (Oregon and California), Armenia, Iceland, Ethiopia
Learn more: Gem-A gemstone education resources.
Colour Variations
Opaque to translucent volcanic glass, usually black to dark brown.
Optical effects: Sheen (in some varieties)
Detailed Gemology
Mineral species: Natural volcanic glass
Mineral group: Mineraloid
Chemical formula: Natural silica-rich volcanic glass
Mohs hardness: 5.5
Crystal system: Amorphous
Lustre: vitreous
Transparency: opaque
Streak: White
Cleavage: None
Fracture: Conchoidal
Specific gravity: 2.35-2.60
Refractive index: 1.48-1.51
Optical phenomena: Sheen in some varieties (silver or gold sheen)
Colour range: Black, dark brown, grey, occasionally mahogany and sheen varieties
Common inclusions: Flow banding, gas bubbles, cristobalite spherulites
Geological environment: Rhyolitic to dacitic volcanic terrains
Principal mining regions: Mexico, United States (Oregon and California), Armenia, Iceland, Ethiopia
Important commercial sources: Commercial lapidary obsidian is sourced mainly from Mexico and the western United States
Historical significance: Extensively used in stone tools and ceremonial artifacts.
Common treatments: Generally untreated.
Synthetic or imitation forms: Man-made glass can imitate obsidian.
Common look-alikes: Black glass, jet, onyx
Jewellery uses: Used in carvings, cabochons, beads, and collector material.
Care recommendations: Brittle and fracture-prone; avoid impact and abrasion. Clean gently with mild soap and water.
Cross-check profile data with GIA Gem Encyclopedia and Mindat entry for Obsidian.
Formation
Forms when felsic lava cools too quickly for crystalline mineral growth.
Origin
Commercial lapidary obsidian is sourced mainly from Mexico and the western United States
Uses
Best for: Used in carvings, cabochons, beads, and collector material.
Ideal uses: Cabochons and carvings with protected use due to brittleness.
Care
Brittle and fracture-prone; avoid impact and abrasion. Clean gently with mild soap and water.
Need another candidate? Use advanced gemstone search or return to the identification guide.
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Obsidian FAQ
How can I identify Obsidian?
Compare hardness (5.5 Mohs), crystal system (Amorphous), colour profile, and lustre (vitreous) with your sample. Then cross-check related gemstones listed above.
What colour range does Obsidian appear in?
Opaque to translucent volcanic glass, usually black to dark brown.
Where is Obsidian commonly used?
Cabochons and carvings with protected use due to brittleness.. For maintenance, follow the care guidance in this profile.
Scientific References
GIA: general gemstone identity (reviewed) - Batch 01 factual verification pass.
Gem-A: gemological terminology and testing references (reviewed) - Batch 01 factual verification pass.
Mindat: mineral species and principal localities (reviewed) - Batch 01 factual verification pass.
International Gem Society: gem trade context and treatment overview (reviewed) - Batch 01 factual verification pass.