igneous
Basalt Pebble
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; 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 very near the Earth's surface. This specific specimen is a water-worn river or beach pebble, smoothed by mechanical erosion over time.
Uses & applications
Used in construction as aggregate, in road building, and in concrete. Smooth pebbles like this are popular in aquarium landscaping and rock tumbling hobbies.
Geological facts
Basalt is the most common volcanic rock on Earth and also makes up most of the ocean floors. 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 large crystals. Most common in volcanic regions or as transported pebbles in riverbeds.
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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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