igneous
Basalt Pebble
Basalt (extrusive mafic igneous rock)
AI-generated identification · may be incorrectHardness 5.5-6 Mohs, dark gray to black, dull to sub-metallic luster, fine-grained (aphanitic) texture, specific gravity ~2.8-3.0.
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Physical properties
Hardness 5.5-6 Mohs, dark gray to black, dull to sub-metallic luster, fine-grained (aphanitic) texture, specific gravity ~2.8-3.0.
Formation & geological history
Formed from rapid cooling of magnesium- and iron-rich lava exposed at or near planetary surfaces.
Uses & applications
Commonly used as construction aggregate, asphalt base, railroad ballast, and decorative landscaping stone.
Geological facts
Basalt makes up over 90% of all volcanic rock on Earth and dominates the lunar maria and oceanic crust.
Field identification & locations
Recognized by its dark coloration, heavy mass relative to size, fine-grained matrix, and smooth water-worn surface.
