igneous
Basalt Pebble
Aphanitic Mafic Igneous Rock
Hardness: 6 on Mohs scale; Color: dark grey to dark brownish-purple with subtle banding or alteration lines; Luster: dull to earthy (slightly shiny when wet); Structure: fine-grained (aphanitic) to vesicular or amygdaloidal matrix; Cleavage: none.
- Hardness
- 6 on Mohs scale
- Luster
- dull to earthy (slightly shiny when wet)
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Physical properties
Hardness: 6 on Mohs scale; Color: dark grey to dark brownish-purple with subtle banding or alteration lines; Luster: dull to earthy (slightly shiny when wet); Structure: fine-grained (aphanitic) to vesicular or amygdaloidal matrix; Cleavage: none.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or near the Earth's surface, common along mid-ocean ridges, oceanic islands, and volcanic continental regions.
Uses & applications
Commonly used as construction aggregate, crushed stone for road bases, concrete aggregate, railroad ballast, and landscaping pebbles.
Geological facts
Basalt is the most common rock type in the Earth's crust, covering most of the ocean floors. It is also extremely common on the Moon and Mars.
Field identification & locations
Identified by its dark color, heavy weight relative to size, fine-grained texture, and smooth rounded shape resulting from stream or beach erosion. Widely found along lake shores, riverbeds, and ocean beaches worldwide.
