igneous
Basalt (River Pebble)
Extrusive mafic igneous rock
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained (aphanitic); Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Fine-grained (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 specific specimen has been rounded by fluvial (river) or glacial erosion over thousands of years.
Uses & applications
Used in construction as aggregate, for making rock wool insulation, as road base, and frequently used in landscaping or for decorative river stone features.
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 by its heavy weight (high density), dark color, and fine grain where individual crystals are too small to see with the naked eye. Commonly found on beaches, riverbeds, and near volcanic sites.
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Dark Igneous Rock (Likely Basalt or Diabase)
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