Basalt

Hardness: 6 (Mohs scale), Color: Dark grey to black, Luster: Dull to earthy, Crystal structure: Aphanitic (fine-grained), Cleavage: None, Specific gravity: 2.8-3.0

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. Most common rock on Earth's crust.

Extensively used in construction (crushed stone for road bases and concrete aggregate), railroad ballast, and high-quality stone pavers.

Basalt also makes up most of the ocean floor and is the primary rock found on the Moon's lunar maria and Mars.

Identify by its dark color, heavy weight (density), and fine-grained texture. It often shows vesicles (tiny holes from gas bubbles) in larger specimens. Found globally in volcanic regions and ocean basins.