igneous
Basalt (Weathered)
Mafic Igneous Rock
Hardness: 5-6 (Mohs), Color: Dark grey to brownish-tan when weathered, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.8–3.0
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Physical properties
Hardness: 5-6 (Mohs), Color: Dark grey to brownish-tan when weathered, Luster: Dull/Earthy, Crystal Structure: Aphanitic (fine-grained), Cleavage: None, Specific Gravity: 2.8–3.0
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 be a water-worn or weathered pebble likely from the Cenozoic era.
Uses & applications
Used primarily in construction for road base, concrete aggregate, and railroad ballast. Exceptionally durable for architectural stonework.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identify in the field by its heavy weight (high density), dark interior color if chipped, and fine-grained texture. Commonly found in volcanic regions or riverbeds downstream from volcanic sources.
