igneous
Vesicular Basalt
Extrusive Mafic Igneous Rock (composed of Plagioclase feldspar, Pyroxene, and Olivine)
Hardness: 5-6 (Mohs scale); Color: Dark grey, black, or dark brown; Luster: Dull to earthy; Structure: Vesicular (contains numerous small gas bubbles or holes); Specific Gravity: 2.8 - 3.0
- Hardness
- 5-6 (Mohs scale)
- Color
- Dark grey, black, or dark brown
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark grey, black, or dark brown; Luster: Dull to earthy; Structure: Vesicular (contains numerous small gas bubbles or holes); Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (mafic) at the Earth's surface. The holes (vesicles) are created by gas bubbles trapped in the lava as it solidifies. Can range from modern volcanic eruptions to billions of years old.
Uses & applications
Used in construction as road aggregate, railroad ballast, and concrete. Vesicular varieties are often used in landscaping, as BBQ grill stones, or for artisanal stone carving.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large-scale basalt flows can create unique hexagonal columns, such as those at the Giant's Causeway.
Field identification & locations
Identify in the field by its dark color, heavy weight (relative to size, unless very porous), and the presence of small circular pits (vesicles). Found globally in volcanic regions like Hawaii, Iceland, and the Pacific Northwest of the USA.
