igneous
Basalt (River Pebble)
Extrusive mafic igneous rock
Hardness: 6.0; Color: Dark grey to black; Luster: Dull or earthy; Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8–3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull or earthy
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Physical properties
Hardness: 6.0; Color: Dark grey to black; Luster: Dull or earthy; 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 very near the Earth's surface. This specific specimen has been rounded by fluvial (river) erosion over many years.
Uses & applications
Commonly used as aggregate in construction, road base, railroad ballast, and sometimes in decorative landscaping 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 extensively on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture lacking visible crystals. Very common in volcanic regions and riverbeds.
