igneous
Vesicular Basalt
Extrusive mafic igneous rock (primarily Plagioclase feldspar and Pyroxene)
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained) with visible gas bubbles (vesicles); Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull/earthy
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained) with visible gas bubbles (vesicles); Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. The holes (vesicles) are created by gas bubbles that were trapped in the lava as it solidified. Geological age varies from Pre-Cambrian to modern volcanic eruptions.
Uses & applications
Used extensively in construction as aggregate for road base and concrete, as decorative landscaping stone (lava rock), and sometimes as an abrasive (scoria) in industrial stone-washing for textiles.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large-scale basaltic lava flows can form unique geometric columns, such as those at the Giant's Causeway in Ireland.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size), and characteristic 'pock-marked' or holey surface. Common in volcanic regions such as Iceland, Hawaii, and the Pacific Northwest of the USA.
