igneous
Basalt (River-Worn Pebble)
Basalt
Hardness: 6; Color: Dark grey to black; Luster: Dull to sub-metallic; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6; Color: Dark grey to black; Luster: Dull to sub-metallic; 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 specific specimen has been rounded and smoothed by water transport in a river or coastal environment.
Uses & applications
Commonly used as crushed stone for aggregate in construction, road base, and railroad ballast. Some smooth basalt stones are used in massage therapy (hot stones) or decorative landscaping.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up most of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identifiable by its dark color, heavy weight (relative to size), and fine-grained texture. To distinguish from similar rocks, look for the absence of visible quartz crystals and a high density.
