Basalt

Hardness of 6 on the Mohs scale, dark gray to black in color, fine-grained aphanitic texture, sub-conchoidal fracture, specific gravity of 2.8-3.0.

Formed from the rapid cooling of low-viscosity, magnesium- and iron-rich lava exposed at or very near the surface of a planet or moon.

Commonly used in construction as crushed stone for road base, concrete aggregate, railroad ballast, and in the manufacturing of rock wool insulation.

Basalt is the most common rock type in the Earth's crust underlying the ocean basins, and it is also found extensively on the Moon, Mars, and Venus.

Easily identified in the field by its dark, dense, fine-grained appearance, often showing tiny visible mineral crystals or vesicles (gas bubbles) if it is vesicular basalt. Found worldwide in volcanic provinces.