igneous
Dark fine-grained volcanic rock, likely basalt
Basalt (mafic, aphanitic igneous rock)
AI-generated identification · may be incorrectDark gray to black, rough and fine-grained with no obvious crystals; typically Mohs hardness about 6, dull to slightly vitreous, with no visible cleavage. Common minerals are plagioclase feldspar and pyroxene, sometimes olivine; density is usually about 2.8–3.0 g/cm³.
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Physical properties
Dark gray to black, rough and fine-grained with no obvious crystals; typically Mohs hardness about 6, dull to slightly vitreous, with no visible cleavage. Common minerals are plagioclase feldspar and pyroxene, sometimes olivine; density is usually about 2.8–3.0 g/cm³.
Formation & geological history
Forms when iron- and magnesium-rich lava cools quickly at or near Earth’s surface; basalt occurs from geologically recent eruptions through ancient volcanic terrains.
Uses & applications
Used as crushed aggregate, roadstone, railway ballast, and building stone; attractive pieces may be kept as specimens.
Geological facts
Basalt is among Earth’s most abundant volcanic rocks and forms much of the ocean floor.
Field identification & locations
The image shows a small, angular, uniformly dark specimen consistent with basalt, though visual identification alone cannot confirm it. Look for a dense, fine-grained texture and test for hardness; basalt is common in volcanic regions and oceanic crust.
