igneous
Basalt Pebble
Extrusive mafic igneous rock
Hardness: 6 on Mohs scale; Color: dark grey to black or brownish-grey from weathering; Luster: dull to sub-vitreous; Texture: fine-grained (aphanitic), stream-rounded pebble shape; Specific gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Color
- dark grey to black or brownish-grey from weathering
- Luster
- dull to sub-vitreous
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Physical properties
Hardness: 6 on Mohs scale; Color: dark grey to black or brownish-grey from weathering; Luster: dull to sub-vitreous; Texture: fine-grained (aphanitic), stream-rounded pebble shape; 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. Stream or beach erosion subsequently rounded the rock into a pebble.
Uses & applications
Commonly used in crushed stone aggregate, construction, road base, landscaping, and asphalt paving.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the oceanic crust. It is also found abundantly on the Moon, Mars, and Venus.
Field identification & locations
Identified in the field by its dark color, fine-grained texture, and lack of visible quartz. Highly abundant along beaches, riverbeds, and volcanic regions worldwide.
