igneous
Basalt (River Rock pebble)
Basalt (a mafic extrusive igneous rock)
Hardness: 6 (Mohs scale). Color: Dark grey to greenish-black. Luster: Dull or earthy. Structure: Fine-grained (aphanitic) with microscopic crystals. Specific Gravity: 2.8–3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to greenish-black
- Luster
- Dull or earthy
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Physical properties
Hardness: 6 (Mohs scale). Color: Dark grey to greenish-black. Luster: Dull or earthy. Structure: Fine-grained (aphanitic) with microscopic crystals. Specific Gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron. This specific specimen has been smoothed and rounded by river or stream erosion over many years.
Uses & applications
Used primarily in construction (crushed stone, road base, concrete aggregate), landscaping, and sometimes for hot stone massage therapy due to high heat retention.
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 on the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight compared to other similar-sized rocks, and lack of visible individual crystals without magnification. Commonly found in former volcanic areas or riverbeds downstream from volcanic zones.
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