igneous
Basalt (River Pebble)
Extrusive mafic igneous rock
Hardness: 6 (Mohs); Color: Dark grey to olive-brown; Luster: Dull/Earthy (aphanitic texture); Crystal structure: Fine-grained/Microcrystalline; Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to olive-brown
- Luster
- Dull/Earthy (aphanitic texture)
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to olive-brown; Luster: Dull/Earthy (aphanitic texture); Crystal structure: Fine-grained/Microcrystalline; 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 and smoothed by water erosion in a fluvial (river) environment.
Uses & applications
Used in construction as aggregate, road base, and decorative landscaping. High quality specimens are used for 'hot stone' massage and aquarium decor.
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 on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and lack of visible crystals. Commonly found in volcanic regions or riverbeds downstream from volcanic sources.
