igneous
Basalt
Extrusive Igneous Basalt (contains Plagioclase Feldspar and Pyroxene)
Hardness: 6 (Mohs scale), Color: Dark grey to black (weathered surfaces may be brown), Luster: Dull or sub-metallic, 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 (weathered surfaces may be brown), Luster: Dull or sub-metallic, Crystal structure: Aphanitic (fine-grained), 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. Most common rock in the Earth's crust.
Uses & applications
Extensively used in construction for aggregate, road base, concrete, and railroad ballast. It is also used as a thermal insulator in the form of rock wool and for stone carvings.
Geological facts
Basalt is the most common rock type on the surfaces of Mercury, Venus, the Moon, and Mars. It forms the entirety of the oceanic crust.
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible crystals without a magnifying lens. Commonly found in lava flows, oceanic plates, and shield volcanoes like those in Hawaii or Iceland.
