igneous
Basalt (River Cobble)
Basalt
Hardness: 6 (Mohs); Color: Dark grey to greenish-grey; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to greenish-grey
- Luster
- Dull/Earthy
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to greenish-grey; 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 or near the Earth's surface. This specific specimen has been rounded by mechanical weathering in a river or stream environment.
Uses & applications
Commonly used as aggregate in construction, road base, railroad ballast, and for garden landscaping/river rock drainage.
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 extensively on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture. Commonly found in volcanic regions or in riverbeds downstream from volcanic plateaus.
