igneous
Basalt pebble
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs scale); Color: dark grey to black with some oxidative brown weathering; Luster: dull; Crystal structure: fine-grained (aphanitic); Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs scale)
- Color
- dark grey to black with some oxidative brown weathering
- Luster
- dull
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs scale); Color: dark grey to black with some oxidative brown weathering; Luster: dull; Crystal structure: fine-grained (aphanitic); 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 pebble has been subsequently rounded by water erosion in a river or coastal environment.
Uses & applications
Basalt is used extensively in construction as aggregate, for paving, and as railroad ballast. Smaller smooth pebbles are often used in decorative landscaping or massage therapy.
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
Identified in the field by its dark color, heavy weight (relative to size), and lack of visible large crystals. It often feels denser than sedimentary rocks like shale.
