Vesicular Basalt

Physical Properties

Hardness: 6; Color: dark grey to black; Luster: dull to earthy; Structure: vesicular (porous) with aphanitic groundmass; Cleavage: none; 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 holes (vesicles) are created by gas bubbles trapped in the cooling lava.

Uses & Applications

Used primarily in landscaping, decorative stone, construction aggregate, and occasionally in grill filters or as BBQ lava rocks.

Geological Facts

Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Most of the dark plains on the Moon (Maria) are also composed of basalt.

Field Identification & Locations

Identify by its dark color, heavy weight (relative to size), and characteristic swiss-cheese-like holes. Common in volcanic regions such as Hawaii, Iceland, and the Pacific Northwest.

Identified on: 5/14/2026

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