igneous
Possible basalt or weathered mafic rock
Basalt; chiefly plagioclase feldspar and pyroxene, commonly with olivine and iron oxides
AI-generated identification · may be incorrectDark gray-green, dull to weakly glossy, fine-grained and rounded/weathered; typical hardness is about 5–6 Mohs, with no obvious cleavage and relatively high density (about 2.8–3.1 g/cm³). The image is insufficient to confirm texture or mineral composition.
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Physical properties
Dark gray-green, dull to weakly glossy, fine-grained and rounded/weathered; typical hardness is about 5–6 Mohs, with no obvious cleavage and relatively high density (about 2.8–3.1 g/cm³). The image is insufficient to confirm texture or mineral composition.
Formation & geological history
Basalt forms when mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic flows and oceanic crust. Its age may range from geologically recent to billions of years; the rounded form likely reflects weathering or transport.
Uses & applications
Used as crushed aggregate, road stone, railroad ballast, building stone, and occasionally as a decorative specimen. Ordinary examples have little jewelry or collector value.
Geological facts
Basalt is the most common volcanic rock and makes up much of the ocean floor. Vesicles, visible crystals, or a magnetic response could help distinguish it from related mafic rocks.
Field identification & locations
Look for a uniformly dark, dense rock that may attract a magnet weakly; a glassy surface suggests rapid cooling, while coarse crystals suggest gabbro. Common worldwide, especially volcanic regions and river gravels; a fresh cut surface and hardness test would improve identification.
