Basalt is a common extrusive igneous volcanic rock formed from the rapid cooling of basaltic lava exposed at or very near the surface of earth. Basalt describes the formation in a series of lava basalt flows. Basalt commonly features a very fine-grained or glassy matrix interspersed with visible mineral grains. Basalt is usually grey to black in colour. Basalt with a vesicular texture is called vesicular basalt, when the bulk of the rock is mostly solid; when the vesicles are over half the volume of a specimen, it is called scoria. This texture forms when dissolved gases come out of solution and form bubbles as the magma decompresses as it reaches the surface, yet are trapped as the erupted lava hardens before the gases can escape. 4K UHD 3840×2160 30p.