Basalt (Vesicular/Scoria)

Physical Properties

Hardness: 5-6 Mohs. Color: Dark grey to black or brownish-black. Luster: Dull/Earthy. Crystal structure: Aphanitic (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 (basaltic) erupted from a volcano. The holes or 'vesicles' are formed by trapped gas bubbles escaping as the rock solidifies.

Uses & Applications

Used in construction as road base, aggregate in concrete, landscaping (lava rocks), and sometimes as high-friction paving stones.

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 found extensively on the Moon and Mars.

Field Identification & Locations

Identify by its dark color, heavy weight compared to other porous rocks like pumice, and the presence of small pits or vesicles. Commonly found in volcanic regions such as Hawaii, Iceland, or the Pacific Northwest.

Identified on: 4/20/2026

Mode: Standard