igneous
Basalt (Beach Pebble)
Extrusive mafic igneous rock
Hardness: 6-7 (Mohs scale); Color: Black or dark grey; Luster: Dull/Matte (when dry); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0; Texture: Smooth due to water erosion.
- Hardness
- 6-7 (Mohs scale)
- Color
- Black or dark grey
- Luster
- Dull/Matte (when dry)
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Black or dark grey; Luster: Dull/Matte (when dry); Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0; Texture: Smooth due to water erosion.
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 and smoothed by wave action in a marine or river environment over thousands of years.
Uses & applications
Used in landscaping, massage therapy (hot stones), aquarium decor, and industrially as crushed stone for aggregate in construction and road base.
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 by its dark color, heavy weight for its size, and lack of visible crystals. Commonly found on volcanic coastlines like those in Hawaii, Iceland, or the Pacific Northwest.
