Basalt

Physical Properties

Hardness: 6.0 on Mohs scale. Color: Dark grey to black, often weathering to brownish or green. Luster: Dull to sub-metallic. Crystal Structure: Fine-grained (aphanitic). 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 Earth's surface. Basalt can be found in formations ranging from the Precambrian to current volcanic eruptions.

Uses & Applications

Used widely in construction as crushed stone for road base, railroad ballast, and concrete aggregate. It is also used as dimension stone and for industrial purposes like cast basalt for high-abrasion pipes.

Geological Facts

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

Field Identification & Locations

Identify by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. It can often be found in volcanic regions, oceanic crustal plates, and massive flood basalt provinces.

Identified on: 4/20/2026

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