igneous
Basalt (River Stone)
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull (unless wet/polished); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull (unless wet/polished)
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull (unless wet/polished); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. This specific specimen has been chemically and physically weathered into a smooth 'river stone' shape by water transport over centuries.
Uses & applications
Used in construction as aggregate, for road base, in concrete, and for high-temperature stone wool insulation. Smooth specimens are popular for landscaping, massage stones, and aquarium decor.
Geological facts
Basalt is the most common rock in Earth's crust and makes up most of the ocean floor. It is also found extensively on the Moon and Mars, forming the lunar maria (dark plains).
Field identification & locations
Identify in the field by its heavy weight (density), dark uniform color, and lack of visible large crystals. Common in volcanic regions and riverbeds. Water-worn basalt is often very smooth and oval-shaped.
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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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Magnetite
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Magnetite
Magnetite (Fe3O4)
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