igneous
Polished black-and-gold brecciated stone, likely sheen obsidian or brecciated jasper
Probable volcanic glass (obsidian), SiO₂, with iron-oxide or rhyolitic inclusions; exact identification is uncertain from the photograph
AI-generated identification · may be incorrectVery dark black, highly polished, vitreous luster, with cream, tan, and golden mottling/inclusions. Obsidian has Mohs hardness about 5–5.5, no cleavage, conchoidal fracture, and glassy structure; the rounded form appears tumbled or cabochon-polished.
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Physical properties
Very dark black, highly polished, vitreous luster, with cream, tan, and golden mottling/inclusions. Obsidian has Mohs hardness about 5–5.5, no cleavage, conchoidal fracture, and glassy structure; the rounded form appears tumbled or cabochon-polished.
Formation & geological history
If obsidian, it formed when silica-rich lava cooled rapidly, commonly during the Quaternary or younger volcanic activity. The contrasting patches may represent devitrification, lithic fragments, or iron staining; a jasper identification would instead indicate silica-rich sedimentary replacement.
Uses & applications
Used for cabochons, beads, carvings, ornamental objects, and collections; obsidian historically served for sharp tools and weapons. Common polished pieces typically have modest commercial value.
Geological facts
Obsidian can produce exceptionally sharp conchoidal edges and is technically a volcanic glass rather than a crystalline mineral. The visible golden-brown areas may be sheen or included material, but the image does not establish a named variety.
Field identification & locations
Check for curved conchoidal fracture, glass-like translucence at thin edges, and a streakless surface; test hardness cautiously because glass and some jaspers can look similar. Common sources include Mexico, the western United States, Armenia, and Turkey.
