Igneous
Basalt
Mafic Igneous Rock (primarily Plagioclase Feldspar and Pyroxene)
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Submetallic when fine-grained, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.8-3.0.
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull/Submetallic when fine-grained, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic) at or very near the Earth's surface. Occurs in lava flows across all geological ages on Earth, the Moon, and Mars.
Uses & applications
Extensively used in construction as crushed stone for road base, railroad ballast, and concrete aggregate. Specifically utilized in industrial 'basalt fiber' and high-end floor tiles.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up the entirety of the ocean floor and found in massive continental flood basalt provinces like the Deccan Traps.
Field identification & locations
Identify by its heavy weight, dark color, and lack of visible crystals (unless porphyritic). Commonly found in volcanic regions. Tip: Look for a fine-grained, 'salt and pepper' or uniform dark appearance that does not scratch easily with steel.
