igneous
Likely black obsidian
Volcanic glass; composition broadly rhyolitic (silica-rich), with no crystalline mineral structure
AI-generated identification · may be incorrectBlack, glossy to vitreous, with sharp conchoidal fracture and no cleavage; Mohs hardness about 5–5.5, specific gravity around 2.3–2.6. The specimen appears glassy, but the image alone cannot confirm its identity.
Identified More igneous →
Explore Likely black obsidian in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Black, glossy to vitreous, with sharp conchoidal fracture and no cleavage; Mohs hardness about 5–5.5, specific gravity around 2.3–2.6. The specimen appears glassy, but the image alone cannot confirm its identity.
Formation & geological history
Forms when silica-rich lava cools so rapidly that crystals do not develop, typically at volcanic flows; its age depends on the source eruption.
Uses & applications
Historically used for blades and tools; today used for ornamental objects, jewelry, and collecting.
Geological facts
Obsidian can fracture into exceptionally sharp edges and may contain flow bands or small crystals.
Field identification & locations
Look for a glassy sheen, curved shell-like fracture surfaces, and very sharp edges; common around volcanic regions, including the western United States, Mexico, Iceland, and Japan. Similar-looking industrial glass is possible, so provenance or closer inspection helps.
