Basalt

Hardness of 6 on the Mohs scale, dark gray to black in color, fine-grained (aphanitic) texture, dull to submetallic luster, specific gravity around 2.8-3.0.

Formed from the rapid cooling of low-viscosity basaltic lava exposed at or very near the surface of a planet or moon, often associated with volcanic activity and oceanic crust.

Used extensively in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the production of basalt fiber.

Basalt is the most common rock type in the Earth's crust underlying the oceans and is also abundantly found on the Moon and Mars.

Can be identified in the field by its dark color, heavy feel, and fine-grained texture where individual crystals are rarely visible to the naked eye. Found globally in volcanic regions and ancient lava flows.