Basalt

Physical Properties

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic when fresh; Crystal structure: Aphanitic (fine-grained); Cleavage: None (conchoidal fracture); 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 are from the Cenozoic era, though occurrences date back billions of years.

Uses & Applications

Used extensively in construction as aggregate for roads, railroad ballast, and concrete. It is also used as a raw material for stone wool insulation and in high-quality floor tiles.

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 on the Moon and Mars.

Field Identification & Locations

Identify in the field by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. Commonly found in volcanic regions, oceanic islands, and mid-ocean ridges.

Identified on: 4/14/2026

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