igneous
Basalt with Scoria/Vesicular texture
Vesicular Basalt (primarily Plagioclase feldspar, Pyroxene, and Olivine)
Hardness: 5-6 (Mohs scale); Color: Dark grey to black, often weathering to reddish-brown (as seen in image) due to iron oxidation; Luster: Dull/Earthy; Structure: Aphanitic with vesicles (gas bubbles); Specific Gravity: 2.8–3.0.
- Hardness
- 5-6 (Mohs scale)
- Luster
- Dull/Earthy
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Physical properties
Hardness: 5-6 (Mohs scale); Color: Dark grey to black, often weathering to reddish-brown (as seen in image) due to iron oxidation; Luster: Dull/Earthy; Structure: Aphanitic with vesicles (gas bubbles); 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 during volcanic eruptions. The holes (vesicles) are created by trapped gas bubbles that escaped as the lava solidified. They can range from recent to billions of years old.
Uses & applications
Commonly used in construction as aggregate for roads, railroad ballast, and concrete. Highly vesicular varieties (Scoria) are used in landscaping, gas grills, and as abrasive polishing stones.
Geological facts
Basalt is the most common rock type in the Earth's crust as it makes up most of the ocean floor. It is also found on the Moon and Mars, where large basaltic plains are known as 'maria'.
Field identification & locations
Identify in the field by its weight (relatively heavy for its size), dark interior when broken, and the presence of small spherical or oval pits. It is found in volcanic regions worldwide, such as the Pacific Northwest (USA), Iceland, and Hawaii.
