Pliny used the word basalt and it is said to have had an Ethiopian origin, meaning a black stone.
It is a common gray to black volcanic rock. It is usually fine-grained due to rapid cooling of lava on the Earth’s surface.
The shape, structure and texture of a basalt is dependant on the way it erupted and where it erupted – whether into the sea, in an explosive cinder eruption or as creeping lava flows.
Basalt which erupts under open air forms three distinct types of lava or volcanic deposits: scoria, ash or cinder; breccia and lava flows.
Basalt in the tops of lava flows and cinder cones will often be highly vesiculated, imparting a lightweight “frothy” texture to the rock. Basaltic cinders are often red, coloured by oxidised iron from weathered iron-rich minerals such as pyroxene.
Perhaps the most famous basalt flow in the world is the Giant’s Causeway on the northern coast of Ireland, in which the vertical joints form hexagonal columns and give the impression of having been artificially constructed.