igneous
Basalt River Pebble
Basalt (Mafic Volcanic Rock)
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Sub-metallic (when wet); Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull/Sub-metallic (when wet)
Identified More igneous →
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Physical properties
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Sub-metallic (when wet); 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 specific specimen has been rounded by fluvial erosion in a river or stream during the Quaternary period.
Uses & applications
Commonly used as crushed stone for construction, railroad ballast, and decorative landscaping stones. Highly polished versions are used in hot stone massage therapy.
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
Identified by its dark color, heavy weight for its size, and lack of visible crystals. Commonly found in volcanic regions and riverbeds downstream from volcanic plateaus.
