igneous
Basalt Beach Pebble
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline (aphanitic); Specific gravity: 2.8–3.0. This specimen shows a smooth, water-worn texture.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline (aphanitic); Specific gravity: 2.8–3.0. This specimen shows a smooth, water-worn texture.
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 pebble was subsequently shaped and polished by wave action in a high-energy coastal environment.
Uses & applications
Commonly used as decorative garden stones, in massage therapy (hot stones), and as aggregate in construction when found in large quantities.
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
Identified by its dark color, heavy weight for its size, and absence of visible large crystals. Commonly found on volcanic coastlines like those in Iceland, Hawaii, or the Pacific Northwest.
