Basalt

Physical Properties

Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to 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. It can be found in oceanic crust and continental flood basalts.

Uses & Applications

Commonly used in construction as crushed stone for road base, concrete aggregate, and railroad ballast. It is also used in the manufacturing of stone wool insulation and occasionally for sculpture or as a decorative stone.

Geological Facts

Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. It is also common on other inner planets like Mars and Venus, as well as the Moon.

Field Identification & Locations

Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows columnar jointing or vesicular (hole-filled) structures if gas was trapped during cooling.

Identified on: 5/2/2026

Mode: Standard