igneous
Basalt (tumbled/river-worn)
Mafic volcanic rock (primarily plagioclase feldspar and pyroxene)
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: Non-existent; Specific Gravity: 2.8–3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: Non-existent; Specific Gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. This specimen appears water-worn, suggesting a secondary transport process in a river or coastal environment.
Uses & applications
Commonly used as aggregate in construction (roads/concrete), for industrial stone wool insulation, and occasionally in decorative landscaping or as grounding stones in 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 prevalent on Mars and the Moon.
Field identification & locations
Identify in the field by its heavy weight relative to size and dark, uniform color. It lack visible grains to the naked eye. Often found in volcanic regions or as smooth pebbles in riverbeds.
