igneous
Basalt (with possible quartz/calcite inclusion)
Extrusive mafic igneous rock
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None (conchoidal fracture)
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None (conchoidal fracture)
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specimen appears to have a small secondary mineral inclusion or surface weathering.
Uses & applications
Commonly used as aggregate in construction, road base, and concrete; fine specimens are used in landscaping or aquarium decor.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up the majority of the ocean floor. It is juga found on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (high density), and lack of visible large crystals. Most common in volcanic regions and oceanic crustal exposures.
