igneous
Basalt Beach Pebble
Basalt (Mafic volcanic rock)
Hardness: 6; Color: Dark grey to greenish-black; Luster: Dull to sub-vitreous; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0
- Hardness
- 6
- Color
- Dark grey to greenish-black
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 6; Color: Dark grey to greenish-black; 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 the earth's surface. This specimen has been naturally polished by water and sand abrasion in a high-energy beach environment.
Uses & applications
Basalt is used as crushed stone for road base, railroad ballast, and in the production of high-strength concrete and stone wool insulation. Decorative pebbles are used in landscaping and aquariums.
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 in the field by its dark color, fine grain, and high density. Beach-worn specimens will be smooth and often take a high polish when wet. Commonly found on volcanic island beaches or ancient rift zones.
