Basalt

Hardness 6 on Mohs scale, dark gray to black, dull to earthy luster, fine-grained (aphanitic) texture, specific gravity 2.8–3.0.

Formed by the rapid cooling of low-viscosity, magnesium- and iron-rich lava at or near the Earth's surface or ocean floor.

Widely crushed for use as aggregate in construction, road base, asphalt, and concrete, as well as polished for architectural slabs.

Basalt is the most abundant bedrock on Earth, making up the vast majority of oceanic crust, and forms lunar maria on the Moon.

Identified in the field by its uniform dark color, fine-grained density, and occasional microscopic vesicular pockets; widespread in volcanic provinces like Hawaii and the Columbia River Plateau.