igneous
Basalt Pebble
Basalt (Extrusive Mafic Rock)
Hardness: 6-7 on Mohs scale; Color: dark gray to black; Luster: dull to earthy; Crystal structure: aphanitic (fine-grained); Specific gravity: 2.8–3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- dark gray to black
- Luster
- dull to earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: dark gray to black; Luster: dull to earthy; Crystal structure: aphanitic (fine-grained); 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 specimen appears to be a river-worn or beach-worn pebble.
Uses & applications
Commonly used as crushed stone for road base, concrete aggregate, railroad ballast, and sometimes for hot stones in massage therapy or decorative landscaping.
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 in large quantities on the Moon and Mars.
Field identification & locations
Identify by its heavy weight relative to size, dark color, and fine-grained texture. Commonly found in volcanic regions, riverbeds, and coastal areas.
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Dark Igneous Rock (Likely Basalt or Diabase)
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