Basalt

Hardness of 6 on the Mohs scale, typically dark gray to black in color, with an aphanitic or fine-grained texture. Composed mainly of plagioclase feldspar and pyroxene.

Formed from the rapid cooling of low-viscosity lava flows rich in iron and magnesium on the Earth's surface. Common in oceanic crust and volcanic regions.

Used heavily in construction as crushed stone for aggregate, railroad ballast, and road construction. Also utilized in manufacturing stone wool insulation.

Basalt is the most common rock type on the Earth's surface and also forms massive extensive flows on the Moon and Mars. Its fine-grained nature results from fast cooling preventing large crystals from forming.

Identify in the field by its dark color, heavy weight, and fine-grained texture lacking visible crystals. Found abundantly globally in volcanic provinces and oceanic islands.