igneous
Basalt River Cobble
Basalt (Aphanitic extrusive mafic igneous rock)
Hardness: 6.0; Color: Dark grey to charcoal; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0
- Hardness
- 6
- Color
- Dark grey to charcoal
- Luster
- Dull/Matte
Identified More igneous →
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Physical properties
Hardness: 6.0; Color: Dark grey to charcoal; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Cleavage: None; 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. This specific specimen has been rounded by fluvial (river) or glacial transport.
Uses & applications
Used as construction aggregate, road base, river rock for landscaping, and occasionally for stonemasonry or garden decor.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large-scale cooling of basalt can form impressive hexagonal columns, such as at the Giant's Causeway.
Field identification & locations
Identify by its heavy weight (high density), fine grain, and dark color. It is commonly found in volcanic regions, riverbeds, and as decorative stone in residential landscaping.
