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

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 basalt on Earth was formed after the Precambrian era, especially along mid-ocean ridges.

Uses & Applications

Used extensively in construction as an aggregate for asphalt and concrete, as road base, railroad ballast, and for architectural stonework such as floor tiles and garden features.

Geological Facts

Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. It is juga found on the Moon (the dark lunar maria) and Mars.

Field Identification & Locations

Identify in the field by its high density, dark color, and fine-grained texture lacking visible quartz. Often exhibits columnar jointing in large outcrops. Common in volcanic regions.

Identified on: 4/27/2026

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