igneous
Basalt Pebble
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6 on Mohs scale; Color: Dark grey to blackish; Luster: Dull to sub-metallic; Texture: Aphanitic (fine-grained), water-worn and rounded; Specific Gravity: ~2.8-3.0.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to blackish
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to blackish; Luster: Dull to sub-metallic; Texture: Aphanitic (fine-grained), water-worn and rounded; 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 surface of a terrestrial planet or moon. This specific piece has undergone mechanical weathering and river or beach transport to form a rounded pebble.
Uses & applications
Commonly used as construction aggregate, crushed stone for road bases, concrete aggregate, and decorative landscaping stone. Small worn pebbles are often collected as river rocks.
Geological facts
Basalt is the most common rock type in the Earth's crust, underlying most of the ocean basins. It also makes up large areas of the Lunar maria on the Moon and dominates the surface of Mars.
Field identification & locations
Identified in the field by its dark color, fine grain, and heavy feel for its size (mafic composition). Very common along gravel riverbeds, ocean beaches, and volcanic terrains worldwide.
