igneous
Basalt Pebble
Mafic Igneous Rock (Basalt)
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull or matte; Structure: Fine-grained (aphanitic); Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black
- Luster
- Dull or matte
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull or matte; 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 exposed at or very near the Earth's surface. This specimen has been rounded by fluvial or wave erosion.
Uses & applications
Crushed basalt is used in construction for road base, concrete aggregate, and railroad ballast. Small tide-worn pebbles are used in landscaping and aquariums.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floors. It is also common on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and lack of visible crystals. Found commonly on volcanic beaches, riverbeds, and oceanic islands.
