igneous
Gravel (likely Basalt or Greywacke)
Basalt (Mafic volcanic rock)
Hardness: 6-7 Mohs; Color: Dark grey to charcoal; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- Dark grey to charcoal
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to charcoal; Luster: Dull to 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 near the Earth's surface. These small fragments are often mechanically crushed for industrial use.
Uses & applications
Primary use is in construction as road base, railroad ballast, and aggregate in concrete or asphalt.
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
Identified by its dark color, heavy weight for its size, and lack of visible crystals. It is ubiquitous in crushed stone quarries globally.
