Rock · Volcanic glass
Obsidian
SiO2-rich volcanic glass
Obsidian is rhyolitic volcanic glass, black, with snowflake (cristobalite spherulites), rainbow and mahogany varieties from Oregon (Glass Buttes), Mexico, Armenia and Iceland; 'Apache tears' are rounded nodules from Arizona. It is a rock, sold as tumbled stones, spheres and knapped blades, and its conchoidal fracture gives razor edges. Collecting on Glass Buttes BLM land is allowed for personal use within the 250 lb annual limit.
| Formula | SiO2-rich volcanic glass |
|---|---|
| IMA status | rock |
| Crystal system | Amorphous |
| Mohs hardness | 5–5.5 |
| Group | Volcanic glass |
| Type locality | None |
Fakes and treatments
Coloured 'obsidian' in blue, green or gold sheen without a stated locality is usually slag glass or manufactured glass; natural obsidian is black, brown or grey with sheen from inclusions.
Elsewhere
- Wikidata: Q53754
- Wikipedia: obsidian
- Mindat: Obsidian
Cite this article
Stratum Study. "Obsidian" (Mineral). Stratum Study pack 2026.09, as of 2026-09-19. https://stratum.black/study/minerals/obsidian. Accessed 2026-09-20.
@misc{stratum-obsidian,
title = {Obsidian},
author = {{Stratum Study}},
howpublished = {\url{https://stratum.black/study/minerals/obsidian}},
year = {2026},
note = {Mineral article, Stratum Study pack 2026.09, as of 2026-09-19; sources: stratum, wikidata, commons. Accessed 2026-09-20.}
} Citations carry the pack version and the article's as-of date so they resolve to the same text later. The facts themselves belong to the sources listed below; cite those for the science.