igneous
Likely green obsidian or dark green volcanic glass
Obsidian, a rhyolitic volcanic glass; exact identification requires testing
AI-generated identification · may be incorrectTypically black to dark green, vitreous luster, amorphous (non-crystalline), no cleavage, and conchoidal fracture with sharp edges; hardness about 5–5.5 Mohs and specific gravity roughly 2.3–2.6. The pictured rough surface may also reflect weathering or flow texture.
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Physical properties
Typically black to dark green, vitreous luster, amorphous (non-crystalline), no cleavage, and conchoidal fracture with sharp edges; hardness about 5–5.5 Mohs and specific gravity roughly 2.3–2.6. The pictured rough surface may also reflect weathering or flow texture.
Formation & geological history
Forms when silica-rich lava cools too rapidly for crystals to grow, generally in volcanic environments younger than a few million years. Green coloration can result from iron, inclusions, or alteration.
Uses & applications
Used for ornaments, cabochons, beads, cutting tools, and decorative objects; prized for attractive translucent green varieties. It has little construction value compared with ordinary volcanic rock.
Geological facts
Obsidian can produce exceptionally sharp edges and was widely used for prehistoric blades and arrowheads. It may weather into a dull, devitrified surface over time.
Field identification & locations
Look for glassy luster, very sharp conchoidal breaks, lack of visible mineral grains, and a streakless or pale streak. Common sources include Mexico, the western United States, Armenia, and Turkey; confirm against green jasper, slag, or nephrite with a hardness and specific-gravity test.
