igneous
Polished black stone, possibly basalt or black obsidian
Likely fine-grained basalt (plagioclase and pyroxene) or volcanic glass (obsidian; rhyolitic composition)
AI-generated identification · may be incorrectDark gray-black, smooth polished surface with pale gray mottling and a glassy-to-matte luster; apparent conchoidal-looking break and no visible crystals. Basalt is about Mohs 6, while obsidian is about 5–5.5; specific gravity is roughly 2.5–3.0.
Identified More igneous →
Explore Polished black stone, possibly basalt or black obsidian in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray-black, smooth polished surface with pale gray mottling and a glassy-to-matte luster; apparent conchoidal-looking break and no visible crystals. Basalt is about Mohs 6, while obsidian is about 5–5.5; specific gravity is roughly 2.5–3.0.
Formation & geological history
If basalt, it formed from rapidly cooled mafic lava; if obsidian, from silica-rich lava quenched so quickly that crystals could not grow. Such volcanic rocks are generally Cenozoic to modern, though older examples are widespread.
Uses & applications
Used as decorative stone, cabochons, carvings, and occasionally tools; basalt is also used for aggregate and construction. The specimen appears partly polished and possibly coated or set in a manufactured backing.
Geological facts
The image does not show diagnostic crystals, so exact identification is uncertain. White material may be mineral veins, weathering, polishing compound, or an artificial coating rather than part of the rock.
Field identification & locations
Test an inconspicuous area: obsidian commonly shows sharp conchoidal fracture and glassy edges, whereas basalt feels granular and may reveal tiny crystals under magnification. Common sources include volcanic regions worldwide, including Mexico, the western United States, Iceland, and Italy.
