igneous
Vesicular Basalt
Extrusive Mafic Volcanic Rock
Hardness: 5-6 Mohs. Color: dark gray to black, often weathering to reddish-brown. Luster: dull to sub-metallic. Texture: vesicular (pitted with gas bubbles). Composition: primarily plagioclase feldspar, pyroxene, and olivine.
- Hardness
- 5-6 Mohs
- Color
- dark gray to black, often weathering to reddish-brown
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs. Color: dark gray to black, often weathering to reddish-brown. Luster: dull to sub-metallic. Texture: vesicular (pitted with gas bubbles). Composition: primarily plagioclase feldspar, pyroxene, and olivine.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. The pits (vesicles) are created by trapped gas bubbles that escaped as the lava solidified.
Uses & applications
Commonly used in construction as aggregate, road base, and railroad ballast. In landscaping, it is used for decorative stones and 'lava rocks' for grills. Some specimens are used for stone massage therapy.
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 on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and characteristic holes or 'vesicles'. It reacts poorly to acid and will not scratch glass easily. Commonly found in volcanic fields such as those in Iceland, Hawaii, and the Pacific Northwest.
