igneous
Vesicular Basalt
Basalt (extrusive volcanic rock)
Hardness: 5-6 (Mohs); Color: Dark grey, black, or earthy brown; Luster: Dull/earthy; Texture: Vesicular (contains small cavities/gas bubbles); Composition: Plagioclase feldspar, pyroxene, and olivine.
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey, black, or earthy brown
- Luster
- Dull/earthy
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey, black, or earthy brown; Luster: Dull/earthy; Texture: Vesicular (contains small cavities/gas bubbles); Composition: Plagioclase feldspar, pyroxene, and olivine.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The small holes (vesicles) were created by gas bubbles trapped in the lava as it solidified. Usually occurs in volcanic regions or oceanic crust.
Uses & applications
Used as an aggregate in construction (roads, concrete), as a decorative landscaping stone, in thermal insulation, and occasionally in grill scrubbers or as scoria in fire pits.
Geological facts
Basalt is the most common rock in the Earth's crust and makes up most of the ocean floor. Large areas of the Moon's surface, the lunar maria, are also composed of basalt.
Field identification & locations
Identified by its heavy weight (density), dark color, and characteristic 'pitting' from gas bubbles. Often feels slightly rough or abrasive. Found in volcanic flow fields or as stream-rolled cobbles.
