Basalt

Physical Properties

Hardness: 6; Color: Dark grey to black, weathering to brown or rust; Luster: Dull to 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 very near the Earth's surface. Found in volcanic provinces and oceanic crust worldwide.

Uses & Applications

Used primarily in construction for road base, concrete aggregate, railroad ballast, and dimension stone for pavers or monuments.

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 common on the Moon and Mars.

Field Identification & Locations

Identify in the field by its dark color, heavy weight (relative to volume), and fine-grained texture. It often shows vesiculated (holey) or porphyritic textures.

Identified on: 5/3/2026

Mode: Standard