Vesicular Basalt

Physical Properties

Hardness: 5-6 (Mohs scale), Color: Dark gray to black, often weathering to brown, Luster: Dull/Earthy, Structure: Fine-grained with visible 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. The pits or 'vesicles' are created by trapped gas bubbles that escaped as the lava solidified. They are found in volcanic regions of all ages, from Precambrian to modern-day.

Uses & Applications

Used primarily in construction as crushed stone for road base, concrete aggregate, and railroad ballast. Highly vesicular varieties like scoria are used for landscaping and gas grill stones.

Geological Facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. The vesicles can sometimes be filled with secondary minerals like quartz or calcite, becoming 'amygdules'.

Field Identification & Locations

Identify in the field by its heavy weight (high density), dark color, and characteristic 'pitted' or 'Swiss cheese' texture. Found globally in volcanic hotspots, mid-ocean ridges, and rift valleys.

Identified on: 4/14/2026

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