igneous
Basalt
Basalt (primarily Plagioclase feldspar and Pyroxene)
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Matte to slightly glassy, Crystal structure: Aphanitic (fine-grained), Specific gravity: 2.8–3.0
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Matte to slightly glassy, Crystal structure: Aphanitic (fine-grained), Specific gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity basaltic lava at or very near the Earth's surface. Common in oceanic crust and large volcanic provinces.
Uses & applications
Extensively used as an aggregate in construction, road base, concrete, and railroad ballast; higher-grade specimens are used in architectural stone and stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust and also covers vast areas of the Moon, Venus, and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight, and fine-grained texture with occasional small holes (vesicles). Commonly found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.
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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.
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