igneous
Basalt Pebble
Mafic Igneous Rock (Basalt)
Hardness: 6-7 Mohs; Color: dark grey to black with white speckling; Luster: dull to earthy; Structure: fine-grained (aphanitic) with possible small phenocrysts; Cleavage: none; SG: 2.8-3.0.
- Hardness
- 6-7 Mohs
- Color
- dark grey to black with white speckling
- Luster
- dull to earthy
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: dark grey to black with white speckling; Luster: dull to earthy; Structure: fine-grained (aphanitic) with possible small phenocrysts; Cleavage: none; SG: 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 or marine water erosion.
Uses & applications
Commonly used in crushed form for construction aggregate, road base, and railroad ballast. Smooth pebbles are popular in decorative landscaping and aquarium decor.
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 (density), and fine-grained texture. Found globally in volcanic regions and along coastlines or riverbeds where volcanic material has been transported.
