Basalt

Physical Properties

Hardness: 6 (Mohs scale); Color: Dark gray to black; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); 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. It is the most common rock type in the Earth's crust, making up most of the ocean floor.

Uses & Applications

Used extensively in construction as crushed stone for road base, railroad ballast, and concrete aggregate. High-quality specimens are used in stone carving and architecture.

Geological Facts

Basalt is found across the solar system; it makes up the 'maria' (dark plains) on the Moon and much of the surface of Mars and Venus.

Field Identification & Locations

Identify by its dark color, heavy weight for its size, and microscopic crystal structure. Often found near volcanic activity sites and coastal areas. Commonly used as 'river rocks' in landscaping.

Identified on: 4/20/2026

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