Basalt

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

Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron (mafic) exposed at or very near the surface of a planet or moon. Can range in geological age from recent volcanic eruptions to billions of years old.

Used extensively in construction (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 world's oceans, and it is also the primary volcanic rock found on the Moon (forming the lunar maria) and Mars.

Easily identified by its dark color, fine-grained texture, and high density. Commonly found in volcanic regions, oceanic islands, and continental flood basalt provinces worldwide.