Vesicular Basalt with Amygdaloidal Infill

Physical Properties

Hardness: 5-6 (Mohs); Color: Dark grey to black, reddish-brown where oxidized; Luster: Dull to sub-metallic; Structure: Vesicular/aphanitic; 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) were formed by escaping gas bubbles during solidification.

Uses & Applications

Used primarily in construction for road aggregate, concrete, and railroad ballast. Dense varieties are used for stonework and as a base for thermal insulation (stone wool).

Geological Facts

Basalt is the most common rock in the Earth's crust and makes up the majority of the ocean floor. It is also found extensively on the Moon and Mars.

Field Identification & Locations

Identify in the field by its heavy weight (high density), dark color, and characteristic small holes (vesicles) or white mineral infills (amygdules). Often found in volcanic fields or as river cobbles in volcanic regions.

Identified on: 4/29/2026

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