igneous
Basalt River Pebble
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Fine-grained (aphanitic); Specific Gravity: 2.8-3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal 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) erosion over many years.
Uses & applications
Commonly used as high-quality aggregate in construction, road base, and concrete. In polished or pebble form, it is used for landscaping, aquarium decor, and massage stones.
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 in abundance on the Moon and Mars.
Field identification & locations
Identified by its dark color, heavy weight for its size, and lack of visible large crystals. Commonly found in riverbeds in volcanic regions or along coastal shorelines.
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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.
Igneous
Magnetite
Iron(II,III) oxide (Fe3O4)
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Blue Apatite
Apatite (Group), Ca5(PO4)3(F,Cl,OH)
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Sodalite
Sodalite - Na8(Al6Si6O24)Cl2
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Magnetite
Magnetite (Fe3O4)
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