igneous
Basalt with Vesicular/Amygdaloidal Alteration
Extrusive Igneous Rock (Mafic)
Hardness: 6 on the Mohs scale. Color: Dark gray to black exterior with a reddish-brown iron-stained interior. Luster: Dull to sub-vitreous. Crystal structure: Cryptocrystalline to fine-grained aphanitic with mineral infills.
- Hardness
- 6 on the Mohs scale
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on the Mohs scale. Color: Dark gray to black exterior with a reddish-brown iron-stained interior. Luster: Dull to sub-vitreous. Crystal structure: Cryptocrystalline to fine-grained aphanitic with mineral infills.
Formation & geological history
Formed from the rapid cooling of low-viscosity, magnesium- and iron-rich lava flows at the Earth's surface. Voids or vesicles formed by trapped gas bubbles are often later filled with secondary minerals.
Uses & applications
Commonly used in construction, aggregate, road base, and as a decorative stone in landscaping. Of interest to rockhounds and mineral collectors for secondary mineral fillings.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins and also forms massive continental flood basalt provinces like the Columbia River Plateaus.
Field identification & locations
Found worldwide in volcanic regions, oceanic islands, and ancient basaltic flows. Identified in the field by its dark color, fine-grained texture, and sometimes weathering rinds or iron-oxide staining.
