igneous
Basalt
Basalt (Extrusive Mafic Igneous)
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Earthy, Crystal structure: Fine-grained/Aphanitic, Specific Gravity: 2.8 - 3.0
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Earthy, Crystal structure: Fine-grained/Aphanitic, 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 near the Earth's surface. Can be found in oceanic crust and continental flood lava flows.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and high-quality floor tiles or statues.
Geological facts
Basalt is the most common rock on Earth's surface; it also makes up most of the surface of the Moon, Mars, and Venus.
Field identification & locations
Identified by its dark color, heavy weight, and lack of visible individual crystals. Commonly found in volcanic regions such as the Pacific Northwest, Hawaii, and Iceland.
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Blue Apatite
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)
mineral
Sodalite
Sodalite - Na8(Al6Si6O24)Cl2
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Blue Apatite
Apatite (Group), Ca5(PO4)3(F,Cl,OH)
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Magnetite
Magnetite (Fe3O4)
mineral