igneous
Basalt (River Rock)
Basalt (Mafic volcanic rock)
Hardness: 5-6 Mohs. Color: dark grey to black with light speckling. Luster: dull to earthy. Crystal structure: fine-grained (aphanitic). Cleavage: non-existent. Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- dark grey to black with light speckling
- Luster
- dull to earthy
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Physical properties
Hardness: 5-6 Mohs. Color: dark grey to black with light speckling. Luster: dull to earthy. Crystal structure: fine-grained (aphanitic). Cleavage: non-existent. 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. Extrusive igneous rock. This specific specimen has been rounded by fluvial processes (water erosion) in a river or beach environment.
Uses & applications
Basalt is used extensively in construction as aggregate, in road base, and concrete. This specific pebble form is common in landscaping and aquarium decoration.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up the majority of the ocean floor. It is also found in large quantities on the Moon and Mars.
Field identification & locations
Identify by its weight (dense for its size), dark color, and fine texture. It is commonly found in volcanic regions and riverbeds. Look for a heavy, dark rock that doesn't scratch easily with a copper penny.
