Basalt (Crushed Stone)

Physical Properties

Hardness: 6-7 Mohs; Color: Dark grey to black, weathering to 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 exposed at or very near the surface of a terrestrial planet or a moon. This specimen appears to be mechanically crushed aggregate, most likely from the Cenozoic era or older volcanic flows.

Uses & Applications

Extensively used in construction for road base, concrete aggregate, asphalt pavement, and railroad ballast. Also used in architectural stone and high-temperature insulation (capping stone).

Geological Facts

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

Field Identification & Locations

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

Identified on: 4/30/2026

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