igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull/Matte; Structure: Fine-grained (aphanitic); Cleavage: None/Irregular fracture; Specific Gravity: 2.8 - 3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull/Matte
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Physical properties
Hardness: 6.0 on Mohs scale; Color: Dark grey to black; Luster: Dull/Matte; Structure: Fine-grained (aphanitic); Cleavage: None/Irregular fracture; Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity magnesium-rich and iron-rich lava at or very near the Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and ground-up for asphalt. It is also used as a raw material for stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the surface of the Moon and Mars. It covers about 70% of Earth's surface.
Field identification & locations
Identify by its dark color, heavy weight (dense), and lack of visible crystals to the naked eye. Often found in volcanic fields or near ancient lava flows.
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Fluorapatite (Ca5(PO4)3F)
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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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