Obsidian
Last updated: April 2026
A naturally occurring volcanic glass formed when lava cools rapidly.
Obsidian has a specific gravity of 2.40 and a refractive index of 1.480–1.510, with a Mohs hardness of 5.0–5.5. It is singly refractive.
Physical & Optical Properties
RI Range1.480–1.510
SG Range2.30–2.60
SG Typical2.40
Hardness (Mohs)5–5.5
Crystal SystemAmorphous
Optic CharacterSR (Singly Refractive)
Dispersion0.010
Fluorescence LWInert
Fluorescence SWInert
Chelsea FilterInert
PleochroismNone
ColorsBlack, Brown, Green, Multi
SpeciesNatural Glass
Key Differentiators
- Amorphous volcanic glass
- Conchoidal fracture
- Low RI and SG
Treatments
- Surface Coating (galaxy obsidian, iridescent finish)
- Dyeing (enhanced color or sheen)
Price Context
Natural — low ($/ct)$1
Natural — high ($/ct)$5
NotePer carat; volcanic glass; rainbow sheen and snowflake varieties command modest premium
Price context is approximate. Loupewise is not an appraisal tool. Results are indicators, not certified valuations.
Measurement Guides
Identifying an obsidian? Loupewise walks through these tests in order — RI, SG, fluorescence, and more.
Try Loupewise Free →Studying for the GIA, FGA, or FEEG practical? Obsidian is one of the 130 species in Loupewise’s drill and exam pool — practice identifying it from its measured properties under timed exam conditions.
Practice exams →