Basalt

Hardness: 6 (Mohs), Color: Dark gray to black, Luster: Dull to sub-metallic, Crystal Structure: Aphanitic (fine-grained), 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. Typical of oceanic crust and volcanic hotspots.

Extensively used in construction as aggregate for road base, concrete, and asphalt; also used for stone wool insulation and occasionally for decorative landscaping.

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

Identify by its characteristic dark color, heavy weight (relative to size), and lack of visible crystals to the naked eye. Commonly found in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.