igneous
Basalt Pebble
Extrusive Mafic Volcanic Rock
Hardness: 6-7 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte (when weathered); Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8-3.0
- Hardness
- 6-7 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull/Matte (when weathered)
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte (when weathered); Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specific specimen has been rounded by fluvial or marine erosion.
Uses & applications
Commonly used as an aggregate in construction (roads, concrete), for railroad ballast, and polished for decorative landscaping or river-stone jewelry.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and lack of visible crystals. Commonly found in volcanic regions, riverbeds, and along shorelines.
