Obsidian
Obsidian is a volcanic glas mineral prized by collectors for its exceptional color range.
Obsidian is a natural volcanic glass, usually jet-black, formed when silica-rich lava cools too quickly to crystallise.
About Obsidianextended article
Obsidian is a natural volcanic glass, formed when viscous, silica-rich (rhyolitic) lava cools so fast that crystals have no time to grow. Usually glossy jet-black, it breaks with a smooth conchoidal fracture into razor-sharp edges — a property that made it a prized material for tools and blades throughout human prehistory.
Identifying obsidian
Obsidian is a glass, not a mineral, so it has no crystal structure; it is moderately hard (about 5–5.5) with a bright glassy lustre and curved, shell-like fracture. Attractive varieties include snowflake obsidian (with grey-white cristobalite 'snowflakes'), mahogany obsidian (brown and black) and rainbow or sheen obsidian (iridescent from tiny inclusions).
Where it is found
Obsidian occurs around young volcanoes worldwide — the western United States, Mexico, Iceland, Italy (Lipari), Turkey and many other volcanic regions.
For collectors
Clean black glass, well-developed snowflake patterning and strong rainbow sheen are the most sought-after; knapped pieces and natural 'Apache tears' nodules are also popular.
About Obsidian
Obsidian is classified as a volcanic glas mineral and has the chemical formula SiO2-rich volcanic glass (not a crystalline mineral). It crystallizes in the amorphous system and is one of the most visually varied minerals in the collector market.
Identification & care
Crystals commonly develop as massive, flow-banded, nodular. Its color range is broad, including black, dark brown, gray, mahogany (with brown spots), snowflake (with white cristobalite spherulites), and rainbow/sheen (with nanoparticle layers). The luster is vitreous — glassy, the streak is white, and specimens range from opaque to translucent in thin pieces. The cleavage is none (amorphous). The fracture is conchoidal — extremely sharp edges, which aids identification.
Collector context
Collector notes
Among ornamental materials, Obsidian has a recognized place in collections.
Frequently asked questions
What is Obsidian?
Obsidian is a volcanic glas mineral prized by collectors for its exceptional color range.
What is the chemical formula of Obsidian?
The chemical formula of Obsidian is SiO2-rich volcanic glass (not a crystalline mineral).