Basalt

Physical Properties

Hardness: 6.0; Color: Dark grey to black, often weathering to brown or greenish; Luster: Dull to sub-vitreous; 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 at or very near the Earth's surface. Common in oceanic crust and mid-ocean ridges.

Uses & Applications

Used primarily in construction for crushed stone, road base, concrete aggregate, and railroad ballast. Can also be used as a dimension stone for floor tiles and monuments.

Geological Facts

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

Field Identification & Locations

Identify by its dark color, heavy weight (relative to size), and fine-grained texture that lacks visible individual crystals to the naked eye. Found worldwide in volcanic regions.

Identified on: 4/20/2026

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