igneous
Basalt (Weathered River Stone)
Basalt (SiO2 concentration approx. 45-52%)
Hardness (Mohs scale): 6; Color: Dark grey to black, occasionally greenish or brownish when weathered; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Luster
- Dull/Matte
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Physical properties
Hardness (Mohs scale): 6; Color: Dark grey to black, occasionally greenish or brownish when weathered; Luster: Dull/Matte; 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 or very near the Earth surface. This specific specimen appears to be a water-worn or weathered pebble likely from a river or glacial deposit.
Uses & applications
Commonly used in construction as road base, concrete aggregate, and railroad ballast. Due to heat retention, it is also used in hot stone massage therapies.
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 extremely common on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and lack of visible crystals. It is ubiquitous in volcanic regions such as the Pacific Northwest, Iceland, and Hawaii.
