igneous
Basalt (Beach Pebble)
Basalt
Hardness: 5-6 Mohs. Color: Black to dark gray. Luster: Dull to sub-metallic when wet. Crystal structure: Aphanitic (fine-grained), typically too small to see with the naked eye. Specific gravity: 2.8 to 3.0. This specimen shows a smooth, water-worn texture.
- Hardness
- 5-6 Mohs
- Color
- Black to dark gray
- Luster
- Dull to sub-metallic when wet
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Physical properties
Hardness: 5-6 Mohs. Color: Black to dark gray. Luster: Dull to sub-metallic when wet. Crystal structure: Aphanitic (fine-grained), typically too small to see with the naked eye. Specific gravity: 2.8 to 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 near the Earth's surface. This specific piece was further shaped and polished by wave action on a beach, likely originating from volcanic activity millions of years ago.
Uses & applications
Used widely in construction (crushed stone), road base, and as decorative landscaping stones. Tumbled pieces like this are popular for aquarium decor and as wishing stones for collectors.
Geological facts
Basalt is the most common rock 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 heavy weight (high density), dark color, and lack of visible crystals. It is commonly found on volcanic beaches and in glacial till throughout the world.
