Basalt

Physical Properties

Hardness: 6 on Mohs scale; Color: Dark grey to black, can weather to brown/green; Luster: Dull or 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 common rock in Earth's crust, found in oceanic plates and mid-ocean ridges.

Uses & Applications

Extensively used in construction, especially as crushed stone for road base, concrete aggregate, and railroad ballast. It is also used as dimension stone for tiles and landscape features.

Geological Facts

Basalt is the most common rock on Earth's surface and also covers most of the surface of the Moon, Mars, and Venus. On the Moon, the dark plains known as the lunar maria are vast flows of basaltic lava.

Field Identification & Locations

Identify by its dark color, heavy weight (relative to size), and very fine-grained texture. It often shows small round holes called vesicles caused by gas bubbles. Commonly found on beaches, riverbeds, and volcanic regions.

Identified on: 4/16/2026

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