igneous
Fine-grained dark gray rock, likely basalt
Basalt; chiefly plagioclase feldspar, pyroxene, and commonly olivine or iron oxides
AI-generated identification · may be incorrectDark gray, fine-grained, dull to subtly granular surface; typically hardness about 6, no visible cleavage, and specific gravity around 2.8–3.0. The specimen appears dense and possibly vesicle-free, though image resolution limits certainty.
Identified More igneous →
Explore Fine-grained dark gray rock, likely basalt in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Dark gray, fine-grained, dull to subtly granular surface; typically hardness about 6, no visible cleavage, and specific gravity around 2.8–3.0. The specimen appears dense and possibly vesicle-free, though image resolution limits certainty.
Formation & geological history
Basalt forms when low-silica mafic lava cools rapidly at or near Earth’s surface, producing tiny crystals. It is common in volcanic terrains and oceanic crust, ranging from ancient Precambrian flows to recent eruptions.
Uses & applications
Crushed basalt is used for aggregate, road construction, railway ballast, and concrete; larger pieces are used as building and landscaping stone. Unusual textures can have modest collector value.
Geological facts
Basalt is the most abundant volcanic rock and makes up much of the ocean floor. Its dark color reflects abundant ferromagnesian minerals and relatively low quartz content.
Field identification & locations
Identify it by its dark color, compact fine texture, heavy feel, and lack of obvious large crystals; a streak test is usually gray, and it commonly scratches glass. Common locations include Hawaii, Iceland, the Pacific Northwest, and volcanic belts worldwide.
