igneous
Basalt (Weathered River Stone)
Extrusive Mafic Igneous Rock
Hardness: 5-6 (Mohs); Color: Dark grey to charcoal with speckled phenocrysts; Luster: Variable, dull to slightly shiny; Structure: Fine-grained (aphanitic) matrix; Cleavage: None; Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to charcoal with speckled phenocrysts
- Luster
- Variable, dull to slightly shiny
Identified More igneous →
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to charcoal with speckled phenocrysts; Luster: Variable, dull to slightly shiny; Structure: Fine-grained (aphanitic) matrix; 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 very near the surface of a terrestrial planet or moon. This specific pebble has been smoothed by water erosion through fluvial processes.
Uses & applications
Commonly used in construction as aggregate for concrete and asphalt, railroad ballast, and ground cover for landscaping. In some regions, it is used for high-end countertops or architecture.
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 extensively on the Moon and Mars.
Field identification & locations
Identify in the field by its high density, dark color, and lack of visible quartz. River-tumbled specimens like this one are ubiquitous in gravel pits and stream beds across volcanic regions.
