igneous
Basalt Pebble
Extrusive mafic volcanic rock
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull or sub-metallic when polished; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray to black
- Luster
- Dull or sub-metallic when polished
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull or sub-metallic when polished; 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 exposed at or very near the surface of a terrestrial planet or moon.
Uses & applications
Used in construction as aggregate, for road base, concrete, and in decorative landscaping or aquarium 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 on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and absence of visible crystals. Commonly found in coastal areas, river beds near volcanic sites, and oceanic islands.
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Dark Igneous Rock (Likely Basalt or Diabase)
Basalt (extrusive igneous rock) or Diabase (intrusive igneous rock - also known as Dolerite), largely composed of plagioclase feldspar, pyroxene (augite), and sometimes olivine and amphibole. Exact mineralogy would require thin section analysis.
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