Basalt

Hardness: 6.0-7.0 (Mohs scale), Color: Dark grey to black, Luster: Dull to sub-metallic (fine-grained), Structure: Aphanitic (fine-grained) to vesicular, 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. It is the most common volcanic rock on Earth, covering much of the ocean floor and volcanic islands.

Extensively used in construction for aggregate, road base, railroad ballast, and concrete. It is also used as dimension stone and occasionally for stone wool insulation.

Basalt is equivalent in composition to gabbro, but gabbro is a coarse-grained intrusive rock. Large areas of the Moon are paved with basaltic lava flows known as lunar maria.

Identified by its dark color, heavy weight, and very fine-grained texture. It can sometimes contain small green olivine crystals. It is found globally in regions with volcanic activity or seafloor spreading centers.