igneous
Basalt Pebble
Extrusive Igneous Rock
Hardness: 6 on the Mohs scale; Color: Dark gray to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing tiny crystals of plagioclase feldspar and pyroxene; Cleavage: None; Specific Gravity: 2.8 - 3.0
- Hardness
- 6 on the Mohs scale
- Color
- Dark gray to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on the Mohs scale; Color: Dark gray to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often containing tiny crystals of plagioclase feldspar and pyroxene; Cleavage: None; Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity basaltic lava exposed at or very near the Earth's surface, typically from volcanic eruptions. Geological age can range from recent volcanic activity to billions of years old.
Uses & applications
Used widely in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in manufacturing stone wool insulation or architectural tiles.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins, and it is also the primary rock found on the lunar maria (the dark volcanic plains on the Moon) as well as the surface of Mars.
Field identification & locations
Easily identified by its dark gray to black color, fine-grained texture, and heavy feel relative to its size. Water-worn pebbles are commonly found along riverbeds, beaches, and glacial outwashes where they have been smoothed by wave and current action.
