igneous
Basalt (River Rock)
Basalt
Hardness: 6 (Mohs scale), Color: Dark grey to blackish with brownish weathering, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Specific Gravity: 2.8-3.0.
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to blackish with brownish weathering, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. This specific specimen has been rounded by mechanical erosion in a fluvial (river) environment.
Uses & applications
Used primarily as aggregate for construction, railroad ballast, and decorative landscaping. Fine-grained basalt is also used in asphalt and concrete.
Geological facts
Basalt is the most common rock in Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identify by its dark color, fine grain, and weight (more dense than granite). River-tumbled specimens like this are found in stream beds and coastal deposits worldwide.
