Basalt

Physical Properties

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8 - 3.0. Common vesiculated (holed) texture due to trapped gas bubbles.

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Most common in oceanic crust and volcanic islands. Can range from modern eruptions to billions of years old.

Uses & Applications

Used primarily in construction as crushed stone for road base, railroad ballast, and concrete aggregate. Also processed into rock wool (insulation) and used in high-quality architectural stonework or sculptures.

Geological Facts

Basalt is the most common rock type in the Earth's crust, covering most of the ocean floor. It is also found on the Moon, Mars, and Venus. Famous basaltic formations include the Giant's Causeway in Northern Ireland.

Field Identification & Locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often forms hexagonal vertical columns (columnar jointing) or sharp, jagged coastlines as seen in this image. Found globally in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.

Identified on: 4/16/2026

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