igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 on Mohs scale; Color: Black to dark gray; Luster: Dull to sub-metallic; Structure: Fine-grained aphanitic; Cleavage: None; Specific Gravity: 2.8–3.0
- Hardness
- 6 on Mohs scale
- Color
- Black to dark gray
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Black to dark gray; Luster: Dull to sub-metallic; Structure: Fine-grained aphanitic; 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 particular specimen shows river-worn softening and possible quartz veining.
Uses & applications
Primarily used in construction as aggregate for roads and concrete, high-quality slabs for architecture, and occasionally for ground-line carvings.
Geological facts
Basalt is the most common rock type in Earth's crust and also makes up most of the surface of the Moon (the Lunar Maria).
Field identification & locations
Identify by its dark color, heavy weight for its size, and absence of visible large crystals. Commonly found in volcanic regions or as rounded cobbles in riverbeds.
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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
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Magnetite
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