igneous
Basalt (River Pebble)
Aphanitic Mafic Igneous Rock
Hardness: 6-7 (Mohs); Color: Dark grey to black with possible greenish tint; Luster: Dull or earthy; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0
- Hardness
- 6-7 (Mohs)
- Color
- Dark grey to black with possible greenish tint
- Luster
- Dull or earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark grey to black with possible greenish tint; Luster: Dull or earthy; 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 specimen appears water-worn, indicating it was shaped by river or coastal erosion over a long period.
Uses & applications
Commonly used as crushed stone for construction, road base, and railroad ballast. Smooth river-worn basalt is often used in landscaping and massage therapy (hot 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
Identify by its dark color, heavy weight (relative to size), and fine-grained texture. It often feels smooth and dense when tumbled by water. Found globally in volcanic regions and riverbeds transporting volcanic material.
