igneous
Vesicular Basalt (Amygdaloidal)
Vesicular Basalt (Fe-Mg rich extrusive volcanic rock)
Hardness: 5-6 Mohs. Color: Reddish-brown to tan (due to oxidation/weathering). Luster: Dull/Earthy. Structure: Fine-grained with high porosity (vesicles). Cleavage: None. Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Reddish-brown to tan (due to oxidation/weathering)
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 Mohs. Color: Reddish-brown to tan (due to oxidation/weathering). Luster: Dull/Earthy. Structure: Fine-grained with high porosity (vesicles). Cleavage: None. 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 pits or 'vesicles' are caused by gas bubbles escaping the lava during solidification. Weathering over millions of years has oxidized the iron, giving it its current color.
Uses & applications
Commonly used as aggregate in construction, road base, and landscape decoration (lava rocks). In industry, it can be used for stone wool insulation.
Geological facts
Vesicular basalt is the same material found in 'lava rocks' for gas grills. When the vesicles are filled with secondary minerals like quartz or calcite, it is called Amygdaloidal Basalt.
Field identification & locations
Identify in the field by its distinct 'Swiss cheese' texture, light weight compared to solid basalt, and reddish-brown weathered exterior. Common in volcanic regions such as the Pacific Northwest, Hawaii, or Iceland.
