igneous
Basalt (River Rock)
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Fine-grained/Aphanitic; Specific gravity: 2.8-3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull/Matte
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte; Crystal structure: Fine-grained/Aphanitic; Specific gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. This specific specimen has been chemically and physically weathered into a smooth shape through fluvial (river) or coastal water action.
Uses & applications
Commonly used in construction as aggregate, for paving, and in landscaping. Smaller smooth specimens are often used in decorative garden arrangements or as massage stones.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Look for a heavy, dark, fine-grained rock with no visible crystals to the naked eye. Often found in volcanic regions, riverbeds, and beaches.
