igneous
Basalt (River Pebble)
Extrusive Mafic Igneous Rock
Hardness (Mohs scale): 6; Color: Dark grey to black; Luster: Dull to earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8 to 3.0
- Color
- Dark grey to black
- Luster
- Dull to earthy
Identified More igneous →
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Physical properties
Hardness (Mohs scale): 6; Color: Dark grey to black; Luster: Dull to earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8 to 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 specific specimen has been smoothed and rounded by fluvial (river) erosion.
Uses & applications
Commonly used in construction as crushed stone for road bases and concrete aggregate; also used in landscaping and for hot stone massage therapy due to its heat retention.
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 in large quantities on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its dark color, fine-grained texture, and significant weight for its size. Look for it in volcanic regions or in riverbeds downstream from volcanic mountains.
