igneous
Basalt (Vesicular)
Aphanitic Mafic Volcanic Rock
Hardness: 6 (Mohs), Color: Dark grey to reddish-purple (when weathered), Luster: Dull to sub-metallic, Crystal Structure: Microcrystalline, Cleavage: None, Specific Gravity: 2.8 - 3.0. Features numerous small pits or vesicles.
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Physical properties
Hardness: 6 (Mohs), Color: Dark grey to reddish-purple (when weathered), Luster: Dull to sub-metallic, Crystal Structure: Microcrystalline, Cleavage: None, Specific Gravity: 2.8 - 3.0. Features numerous small pits or vesicles.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. The pits (vesicles) are created by gas bubbles escaping from the lava as it solidifies.
Uses & applications
Commonly used as crushed aggregate in construction, road base, railroad ballast, and sometimes in landscaping or as aquarium stones.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up the majority of the ocean floor. It is also found in large quantities on the Moon and Mars.
Field identification & locations
Identified in the field by its dark color, heavy weight compared to similar looking rocks, and the presence of small spherical or elongated holes. Often found in volcanic regions or as rounded pebbles in riverbeds.
