igneous
Vesicular Basalt
Basalt (Extrusive Igneous Rock)
Hardness: 5-6 Mohs. Color: Dark grey to black, weathering to brown. Luster: Dull to sub-metallic. Crystal Structure: Fine-grained/aphanitic with vesicular cavities. Specific Gravity: 2.8–3.0.
- Hardness
- 5-6 Mohs
- Color
- Dark grey to black, weathering to brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs. Color: Dark grey to black, weathering to brown. Luster: Dull to sub-metallic. Crystal Structure: Fine-grained/aphanitic with vesicular cavities. 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 'vesicles' are holes created by gas bubbles escaping the lava during solidification.
Uses & applications
Used extensively in construction as aggregate for concrete and asphalt, road base, railroad ballast, and sometimes as a decorative landscape stone or 'lava rock' for 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 extensively on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and the presence of small holes or pits. Commonly found in volcanic regions like the Pacific Northwest, Hawaii, and Iceland.
