igneous
Basalt (with Porphyritic/Vesicular texture)
Extrusive mafic igneous rock
Hardness: 6 (Mohs), Color: Dark grey to black, Luster: Dull/Sub-metallic, Crystal Structure: Aphanitic (fine-grained) with visible phenocrysts, Specific Gravity: 2.8–3.0
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Physical properties
Hardness: 6 (Mohs), Color: Dark grey to black, Luster: Dull/Sub-metallic, Crystal Structure: Aphanitic (fine-grained) with visible phenocrysts, 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 moon. Most terrestrial specimens are from the Cenozoic era due to seafloor spreading.
Uses & applications
Commonly used in construction as aggregate for concrete and road base, in the manufacturing of floor tiles, and sometimes in stone massage or aquarium decor.
Geological facts
Basalt is the most common rock on Earth's surface and also covers large areas of the Moon (the 'Maria') and Mars. When cooling, it often forms distinct hexagonal columns.
Field identification & locations
Identify by its dark, heavy nature and fine-grained texture. To distinguish from other dark rocks, use a hand lens to look for tiny olivine or plagioclase crystals. Found extensively in oceanic crust and volcanic regions like Hawaii or the Pacific Northwest.
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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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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