igneous
Basalt (River Pebble)
Extrusive mafic igneous rock
Hardness: 5-6 Mohs; Color: dark gray to black; Luster: dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Hardness
- 5-6 Mohs
- Color
- dark gray to black
- Luster
- dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 5-6 Mohs; Color: dark gray to black; Luster: dull to sub-metallic; Crystal 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 the Earth's surface. This specific specimen has been rounded by fluvial (river) or coastal erosion processes.
Uses & applications
Used in construction as aggregate, for paving, in the production of stone wool insulation, and as decorative river stones in landscaping.
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
Identify by its dark color, heavy weight for its size, and lack of visible large crystals. Common in volcanic regions and riverbeds downstream from volcanic mountains.
