igneous
Basalt (River Pebble)
Basalt
Hardness (Mohs scale): 6; Color: Dark grey to black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained); Cleavage: None/Irregular; Specific gravity: 2.8–3.0
- Color
- Dark grey to black
- Luster
- Dull or earthy
Identified More igneous →
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Physical properties
Hardness (Mohs scale): 6; Color: Dark grey to black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained); Cleavage: None/Irregular; Specific gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specimen has been rounded and smoothed by water erosion in a river or coastal environment.
Uses & applications
Crushed basalt is used in construction for road base, concrete aggregate, and railroad ballast. Fine-grained pebbles are often used in landscaping and decorative aquariums.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up the majority of the ocean floor. It is also common on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture. It lacks visible large crystals. Commonly found in volcanic regions and riverbeds transporting volcanic material.
