igneous
Basalt Pebble
Extrusive mafic igneous rock
Hardness: 6-7 on the Mohs scale. Color: Dark gray to black. Luster: Dull to earthy. Texture: Fine-grained (aphanitic), microcrystalline structure from rapid cooling.
- Hardness
- 6-7 on the Mohs scale
- Color
- Dark gray to black
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 on the Mohs scale. Color: Dark gray to black. Luster: Dull to earthy. Texture: Fine-grained (aphanitic), microcrystalline structure from rapid cooling.
Formation & geological history
Formed from the rapid cooling of low-viscosity basaltic lava rich in iron and magnesium at or near the Earth's surface. Rounded through fluvial or coastal erosion.
Uses & applications
Used in construction as crushed stone, concrete aggregate, asphalt paving, and railway ballast. Polished river pebbles are widely used in landscaping and aquariums.
Geological facts
Basalt is the most common rock type in Earth's crust, making up almost the entire oceanic crust. It is also found extensively on the Moon, Venus, and Mars.
Field identification & locations
Identify by its dark gray-to-black color, fine-grained texture, and hardness. It lacks visible large crystals unless porphyritic. Found along riverbeds, beaches, and volcanic terrains worldwide.
