igneous
Basalt (Beach Pebble)
Extrusive mafic igneous rock
Hardness: 6 (Mohs scale); Color: Black to dark gray; Luster: Dull to sub-vitreous; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0
- Hardness
- 6 (Mohs scale)
- Color
- Black to dark gray
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs scale); Color: Black to dark gray; Luster: Dull to sub-vitreous; 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's surface. This specimen appears water-worn and smoothed by wave action on a beach.
Uses & applications
Used extensively in construction as aggregate, for paving, and in 'hot rock' massage therapies. Smaller pebbles are often used in landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the ocean floor and the lunar mare on the Moon.
Field identification & locations
Identify by its heavy weight (high density), dark color, and fine texture. It often shows small pits (vesicles) from gas bubbles. Commonly found on volcanic coastlines.
