igneous
Basalt River Pebble
Basalt
Hardness: 6 on Mohs scale. Color: Dark grey to black. Luster: Dull or earthy. Crystal structure: Aphanitic (fine-grained), typically too small to see with the naked eye. Specific gravity: 2.8–3.0.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull or earthy
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Physical properties
Hardness: 6 on Mohs scale. Color: Dark grey to black. Luster: Dull or earthy. Crystal structure: Aphanitic (fine-grained), typically too small to see with the naked eye. 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 is a water-worn river pebble, shaped by mechanical weathering in a fluvial environment.
Uses & applications
Basalt is used extensively in construction for aggregate, road base, and railroad ballast. Fine-grained pebbles like this are sometimes used in aquarium decor or landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up the majority of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its dark color, heavy weight for its size, and lack of visible crystals. It is commonly found in volcanic regions or in riverbeds downstream from volcanic outcrops.
