igneous
Polished black stone, likely basalt or basaltic glass
Fine-grained basalt (possibly devitrified volcanic glass); mainly plagioclase and pyroxene, with iron-titanium oxides
AI-generated identification · may be incorrectHardness about 5.5–6.5 Mohs; opaque charcoal-black to dark gray, with a glassy-to-dull luster and no visible crystals. The smooth rounded form is human-polished; apparent pits may reflect vesicles or surface inclusions.
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Physical properties
Hardness about 5.5–6.5 Mohs; opaque charcoal-black to dark gray, with a glassy-to-dull luster and no visible crystals. The smooth rounded form is human-polished; apparent pits may reflect vesicles or surface inclusions.
Formation & geological history
Likely volcanic lava that cooled rapidly at or near Earth’s surface, probably Cenozoic or younger; exact age and locality cannot be determined visually. A glassier variety could be basaltic volcanic glass, but it lacks diagnostic conchoidal fracture in this image.
Uses & applications
Used as decorative stone, cabochons, tumbled specimens, landscaping aggregate, and crushed stone for roads and concrete; generally not a jewelry gemstone of high value.
Geological facts
Basalt is the most widespread volcanic rock on oceanic crust and commonly forms lava flows and pillow lavas. Its dark color comes chiefly from ferromagnesian minerals and iron oxides.
Field identification & locations
Test for hardness against glass, inspect a fresh edge for tiny plagioclase grains, and check density (typically about 2.8–3.1 g/cm³); a streak is usually gray to black. Common worldwide, especially volcanic regions and oceanic islands.
