igneous
Basalt
Basalt (composition of plagioclase, pyroxene, and olivine)
Hardness: 6-7 Mohs; Color: dark grey to black (weathered to brown); Luster: dull/earthy; Crystal structure: fine-grained or aphanitic; Specific gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- dark grey to black (weathered to brown)
- Luster
- dull/earthy
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Physical properties
Hardness: 6-7 Mohs; Color: dark grey to black (weathered to brown); Luster: dull/earthy; Crystal structure: fine-grained or 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 specimen appears water-worn, likely tumbled in a river or creek bed.
Uses & applications
Used extensively in construction for aggregate, asphalt, and railroad ballast. Exceptionally durable for road bases.
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 and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight for its size, and microscopic grain size. Found in volcanic regions and riverbeds carrying volcanic runoff.
