Basalt

Physical Properties

Hardness: 6 (Mohs scale); Color: Dark grey to black, weathering to olive-green or brown; 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 (magma) exposed at or very near the surface of a terrestrial planet or a moon. Most common rock type in Earth's crust (oceanic floor).

Uses & Applications

Extensively used in construction as an aggregate (crushed stone), for asphalt pavement, railroad ballast, and high-quality floor tiles. Small specimens are often used for thermal 'hot stone' massages.

Geological Facts

Basalt is the most common rock in the solar system; it makes up the vast majority of the ocean floor and the lunar 'maria' (dark plains) on the moon.

Field Identification & Locations

Identify by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. Often found in volcanic regions or where ancient lava flows have been exposed.

Identified on: 4/20/2026

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