igneous
Basalt Pebble
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs scale); Color: Dark grey to charcoal; Luster: Dull/Earthy (weathered); Crystal structure: Fine-grained/Aphanitic; Cleavage: None visible in hand specimen
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to charcoal
- Luster
- Dull/Earthy (weathered)
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to charcoal; Luster: Dull/Earthy (weathered); Crystal structure: Fine-grained/Aphanitic; Cleavage: None visible in hand specimen
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 by fluvial (river) or coastal (wave) erosion.
Uses & applications
Basalt is used as crushed stone for road base, railroad ballast, and concrete aggregate. When polished, it is used for architectural stone and floor tiles.
Geological facts
Basalt is the most common rock type on the Earth's surface and makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identifiable by its dark color, heavy weight (high density), and lack of visible crystals. Commonly found in volcanic regions, riverbeds, and beaches. For collectors, look for samples with vesicles (air bubbles) or mineral inclusions like olivine.
