igneous
Basalt Pebble
Basalt (Mafic Volcanic Rock)
Hardness: 6 (Mohs scale), Color: Dark grey to black or brownish when weathered, Luster: Dull to sub-metallic, Crystal Structure: Aphanitic (fine-grained), Specific Gravity: 2.8-3.0.
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Physical properties
Hardness: 6 (Mohs scale), Color: Dark grey to black or brownish when weathered, Luster: Dull to sub-metallic, Crystal Structure: Aphanitic (fine-grained), 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 water-worn, smoothed by fluvial (river) action over long periods.
Uses & applications
Crushed basalt is used in construction for road base, concrete aggregate, and railroad ballast. Fine-grained specimens are used for hot stone massage or decorative garden stones.
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 by its dark color, heavy weight for its size (density), and lack of visible large crystals. Commonly found in volcanic regions or riverbeds downstream from volcanic sources.
