igneous
Porphyritic Basalt
Basalt (Extrusive Igneous Rock)
Hardness: 6 (Mohs), Color: Dark grey to purple-grey with lighter phenocrysts, Luster: Dull/Earthy, Texture: Aphanitic with phenocrysts, Specific Gravity: 2.8–3.0
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Physical properties
Hardness: 6 (Mohs), Color: Dark grey to purple-grey with lighter phenocrysts, Luster: Dull/Earthy, Texture: Aphanitic with phenocrysts, Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. The visible crystals (phenocrysts) formed slowly at depth before eruption.
Uses & applications
Used extensively in construction as crushed stone, road base, concrete aggregate, and sometimes in stone carving or as industrial mineral wool.
Geological facts
Basalt is the most common rock on Earth's surface and makes up most of the ocean floor. It is also found in large quantities on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture. Found globally in volcanic regions like Hawaii, Iceland, and the Columbia River Basalt Group.
