igneous
Vesicular Basalt
Extrusive mafic igneous rock
Hardness: 5-6 (Mohs scale); Color: Dark grey, black, or dark brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) with visible vesicles (gas bubbles); Specific Gravity: 2.8 - 3.0
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark grey, black, or dark brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark grey, black, or dark brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) with visible vesicles (gas bubbles); Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic lava) at or very near the Earth's surface. The holes (vesicles) are created by gas bubbles trapped in the cooling magma as pressure decreases during an eruption.
Uses & applications
Used in construction as road aggregate, railroad ballast, and in the manufacturing of stone wool insulation. Also used in landscaping and as 'lava rocks' for gas grills.
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 found in abundance on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and characteristic pitted or 'bubbly' surface. Commonly found in volcanic regions such as Hawaii, Iceland, and the Pacific Northwest.
