igneous
Polished black stone pendant, likely obsidian
Volcanic glass; primarily silica-rich rhyolitic glass (SiO₂), if obsidian
AI-generated identification · may be incorrectBlack to charcoal, vitreous luster, smooth polished surface, amorphous rather than crystalline, with no cleavage; Mohs hardness about 5–5.5 and specific gravity about 2.35–2.65. The image is low-resolution, so black agate, basalt, or another dark lapidary stone cannot be excluded.
Identified More igneous →
Explore Polished black stone pendant, likely obsidian in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Black to charcoal, vitreous luster, smooth polished surface, amorphous rather than crystalline, with no cleavage; Mohs hardness about 5–5.5 and specific gravity about 2.35–2.65. The image is low-resolution, so black agate, basalt, or another dark lapidary stone cannot be excluded.
Formation & geological history
Obsidian forms when silica-rich lava cools extremely rapidly, preventing crystal growth, generally in volcanic environments younger than roughly 20 million years. Common sources include Mexico, the western United States, Armenia, Turkey, and Japan.
Uses & applications
Used for beads, cabochons, carvings, ornaments, and historically exceptionally sharp cutting tools. The pictured specimen appears polished and mounted as jewelry.
Geological facts
Obsidian commonly breaks with sharp conchoidal fractures and may show flow bands, snowflake patterns, or a translucent brown edge. It is technically volcanic glass rather than a conventional crystalline rock.
Field identification & locations
Field identification: glassy luster, uniform black color, conchoidal fracture, and lack of visible grains; it should scratch glass but generally not quartz. Confirmatory testing requires examining an unpolished edge or conducting hardness and specific-gravity tests.
