igneous
Tumbled black stone, likely black obsidian
Obsidian — natural volcanic glass, primarily SiO₂
AI-generated identification · may be incorrectUsually black, vitreous and highly glossy with no visible crystals; Mohs hardness about 5–5.5, conchoidal fracture, no cleavage, and specific gravity around 2.35–2.ಿರಿಯ5. The rounded shape indicates tumbling or polishing.
Identified More igneous →
Explore Tumbled black stone, likely black obsidian in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Usually black, vitreous and highly glossy with no visible crystals; Mohs hardness about 5–5.5, conchoidal fracture, no cleavage, and specific gravity around 2.35–2.ಿರಿಯ5. The rounded shape indicates tumbling or polishing.
Formation & geological history
Forms when silica-rich lava cools so rapidly that crystals cannot grow, commonly during Quaternary volcanic eruptions. Major sources include Mexico, the western United States, Armenia, Iceland, and Japan.
Uses & applications
Used for ornamental carvings, cabochons, beads, polished stones, and historically very sharp blades; it has limited construction use.
Geological facts
Obsidian is technically a mineraloid rather than a true mineral because it lacks a crystal lattice. The dark red-brown translucent areas may indicate mahogany obsidian or internal iron-rich zones.
Field identification & locations
Identify by its glassy luster, uniform dark color, light weight relative to metallic minerals, and curved shell-like fracture; distinguish it from black glass by natural flow bands, inclusions, or translucence at thin edges. Exact identification is uncertain from the photograph alone.
