igneous
Basalt (Stream Pebble)
Mafic Volcanic Rock (composed mainly of plagioclase feldspar and pyroxene)
Hardness: 6-6.5; Color: Dark grey to greenish-black with weathered lighter patches; Luster: Dull to earthy; Texture: Fine-grained (aphanitic), water-worn and rounded; Specific Gravity: ~2.8-3.0
- Hardness
- 6-6
- Color
- Dark grey to greenish-black with weathered lighter patches
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-6.5; Color: Dark grey to greenish-black with weathered lighter patches; Luster: Dull to earthy; Texture: Fine-grained (aphanitic), water-worn and rounded; Specific Gravity: ~2.8-3.0
Formation & geological history
Formed by the rapid cooling of magnesium-rich and iron-rich lava at or near Earth's surface. Subsequent erosion and stream transport rounded the pebble into its present smooth shape.
Uses & applications
Crushed stone for road construction, concrete aggregate, railway ballast, and decorative garden landscaping stones.
Geological facts
Basalt is the most common rock type in Earth's crust, making up most of the ocean floors. It is also found extensively on the Moon (lunar maria) and Mars.
Field identification & locations
Identify by its dark color, heavy density, fine grain size, and rounded, water-smoothed exterior. Widely found in volcanic regions, riverbeds, beaches, and glacial till worldwide.
