igneous
Basalt River Pebble
Basalt (Mafic Volcanic Rock)
Hardness: 5-6 Mohs. Color: Charcoal gray to black with fine white calcite or quartz veining. Luster: Dull to sub-vitreous. Structure: Aphanitic (fine-grained), non-crystalline visible to the eye. Specific gravity: 2.8–3.0.
- Hardness
- 5-6 Mohs
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 5-6 Mohs. Color: Charcoal gray to black with fine white calcite or quartz veining. Luster: Dull to sub-vitreous. Structure: Aphanitic (fine-grained), non-crystalline visible to the eye. Specific gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. This specific specimen has been polished by fluvial (river) or coastal erosion processes, rounding its edges over thousands of years.
Uses & applications
Basalt is used extensively in construction as aggregate for roads and railroads. Polished pebbles like this are popular in landscaping, aquarium decor, and as 'worry stones' for collectors.
Geological facts
Basalt is the most common rock type in the Earth's crust and actually makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identified in the field by its high density, dark color, and fine-grained texture. To confirm, look for a lack of visible large crystals and a heavy feel for its size. High concentrations are found in volcanic regions and riverbeds downstream from volcanic ranges.
