Basalt

Basalt is a fine-grained, dark-colored, extrusive mafic volcanic rock. It is commonly erupted as passive lava flows due to its low viscosity (resulting from high magmatic temperatures and low silica contents). A dominant component of oceanic crust, basalt is the most abundant volcanic rock.

Texture: aphanitic
Composition: mafic (enriched in iron and magnesium)
Color: black, dark gray or dark brown
Cooling Rate: fast, extrusive
Intrusive Equivalent: gabbro
Other Characteristics: weathers to red-brown, hematite/limonite/clay mixture