igneous
Basalt River Pebble
Mafic Volcanic Rock (Basalt)
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Earthy; Texture: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8–3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull/Earthy
Identified More igneous →
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Physical properties
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Earthy; Texture: Aphanitic (fine-grained) to porphyritic; 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 action (river or stream erosion) over thousands of years.
Uses & applications
Used widely in construction for aggregate, road base, and railroad ballast. Smooth pebbles are popular for landscaping, decorative aquariums, and hot stone massage therapy.
Geological facts
Basalt is the most common rock type in Earth's crust; most of the ocean floor is composed of it. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify by its heavy weight (high density), dark matte color, and lack of visible crystals. Commonly found in old volcanic regions and along riverbeds downstream from volcanic mountains.
