igneous
Basalt
Basalt (composition predominately plagioclase feldspar and pyroxene)
Hardness: 6 (Mohs), Color: dark grey to black, Luster: dull to sub-metallic, Crystal Structure: fine-grained (aphanitic), Specific Gravity: 2.8–3.0
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Physical properties
Hardness: 6 (Mohs), 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 exposed at or very near the surface of a terrestrial planet or a moon. It is the most common volcanic rock on Earth.
Uses & applications
Extensively used in construction, specifically as road base, railroad ballast, and aggregate in concrete. High-quality specimens are used in stone masonry and floor tiles.
Geological facts
Basalt makes up most of the Earth's oceanic crust. It is also found on the Moon and Mars. On Earth, it can form massive columns such as the Giant's Causeway in Northern Ireland.
Field identification & locations
Identify by its dark color, heavy weight (dense), and fine-grained texture. It often feels slightly gritty and may contain small vesicles (holes) or phenocrysts.
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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