igneous
Likely basalt or dark volcanic rock
Basalt; predominantly calcium-rich plagioclase and pyroxene, possibly with olivine
AI-generated identification · may be incorrectDark brown to black, fine-grained and dull to weakly vitreous; typically hardness 5–6 Mohs, no obvious cleavage, and specific gravity about 2.8–3.0. The rough, compact texture is consistent with basalt, though the image cannot confirm composition.
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Physical properties
Dark brown to black, fine-grained and dull to weakly vitreous; typically hardness 5–6 Mohs, no obvious cleavage, and specific gravity about 2.8–3.0. The rough, compact texture is consistent with basalt, though the image cannot confirm composition.
Formation & geological history
Forms when mafic lava cools rapidly at or near Earth’s surface, commonly in volcanic flows and oceanic crust. Basalt ranges from ancient Precambrian formations to actively forming material at modern volcanoes.
Uses & applications
Used as crushed aggregate, road base, railway ballast, riprap, and dimension stone; attractive polished pieces may be used decoratively. Ordinary hand specimens have little commercial value.
Geological facts
Basalt is Earth’s most abundant volcanic rock and makes up much of the ocean floor. Vesicles, if present, may later be filled by minerals such as zeolite, calcite, or quartz.
Field identification & locations
Look for a dense dark color, fine grains, and possible tiny feldspar crystals or gas bubbles; it is not attracted to a magnet unless iron-rich minerals are abundant. Common worldwide, especially volcanic regions and oceanic islands.
