igneous
Vesicular Basalt
Basalt (Extrusive Mafic Igneous)
Hardness: 5-6 (Mohs), Color: Dark grey to black with reddish-brown oxidation, Luster: Dull/Earthy, Structure: Fine-grained/Aphanitic with vesicles (gas bubbles), Specific Gravity: 2.8-3.0
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Physical properties
Hardness: 5-6 (Mohs), Color: Dark grey to black with reddish-brown oxidation, Luster: Dull/Earthy, Structure: Fine-grained/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 at or very near the Earth's surface. The pits or holes (vesicles) are created by gas bubbles trapped in the cooling lava. Most basalt flows date from the Cenozoic era.
Uses & applications
Used extensively in construction as aggregate for concrete and asphalt, railroad ballast, and ground cover. Sometimes used in therapeutic hot stone massage.
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 common on the Moon and Mars.
Field identification & locations
Identified by its heavy weight (density), dark color, and characteristic holes. Often found in volcanic regions, oceanic islands, and mid-ocean ridges. Collectors look for vesicles filled with secondary minerals like zeolites.
