Vesicular Basalt

Physical Properties

Hardness: 6 (Mohs scale); Color: Dark grey, black, or reddish-brown due to iron oxidation; Luster: Dull to earthy; Crystal structure: Aphanitic (fine-grained); Features holes called vesicles formed by gas bubbles.

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic lava) at or very near the Earth's surface. The pits result from trapped volcanic gases escaping as the lava solidifies.

Uses & Applications

Used primarily in construction as aggregate for roads and concrete, in landscaping as 'lava rocks' for moisture retention, and sometimes in 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 extremely common on the Moon and Mars.

Field Identification & Locations

Identify by its dark color, heavy weight (high density), and the presence of small spherical or oval pits (vesicles). Often found in volcanic regions, beaches near volcanic islands, or as glacial till.

Identified on: 5/3/2026

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