igneous
Basalt (Road Gravel)
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull or sub-metallic; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0.
- Hardness
- 6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull or sub-metallic
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull or sub-metallic; Crystal Structure: Aphanitic (fine-grained); 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 to be a common angular fragment used in infrastructure.
Uses & applications
Primarily used as aggregate in construction, road base, asphalt, and railroad ballast due to its high compressive strength and durability.
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 in large quantities on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight for its size, and lack of visible crystals. It is ubiquitous in urban environments as crushed stone.
