Basalt

Physical Properties

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Fine-grained (Aphanitic); Specific Gravity: 2.8–3.0.

Formation & Geological History

Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. Common in oceanic crust and volcanic islands.

Uses & Applications

Extensively used in construction for aggregate, road base, concrete, and railroad ballast. Also used in high-temp insulation (rock wool).

Geological Facts

Basalt is the most common rock in Earth's crust and covers most of the ocean floor. It is also found on the Moon, Mars, and Venus.

Field Identification & Locations

Identify by its heavy weight (high density), dark color, and lack of visible crystals to the naked eye. Found at volcanic sites and ocean ridges.

Identified on: 4/22/2026

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