igneous
Porphyritic basalt
Basalt, likely plagioclase- and pyroxene-bearing
AI-generated identification · may be incorrectDark gray-green, fine-grained volcanic rock with pale mineral grains or patches; typically Mohs 5–6, dull to faintly vitreous, with no obvious cleavage. Exact composition and texture are uncertain from the image alone.
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Physical properties
Dark gray-green, fine-grained volcanic rock with pale mineral grains or patches; typically Mohs 5–6, dull to faintly vitreous, with no obvious cleavage. Exact composition and texture are uncertain from the image alone.
Formation & geological history
Formed when iron- and magnesium-rich lava cooled at or near Earth’s surface; basalt occurs from many geological periods and settings, including oceanic crust and volcanic flows.
Uses & applications
Basalt is used as crushed aggregate, road stone, building stone, and occasionally for decorative objects; this small specimen is mainly suitable for collecting.
Geological facts
The light spots may be larger crystals embedded in a finer volcanic groundmass, a texture called porphyritic.
Field identification & locations
Look for a dense, dark, fine-grained rock with scattered pale crystals; basalt is common in volcanic regions worldwide. A hand lens and streak or hardness tests would help confirm identification.
