Basalt, Vesicular Basalt, Diabase, & Gabbro

Basalt is an extremely common extrusive igneous rock. Most of the sea floor is composed of basalt. Because the magma from which basalt is derived cooled quickly the mineral crystals in the rock had little time to grow seldom reaching more than 1mm in size. Basalt therefore has a fine texture. Often the crystals as so small they are not visible without a magnifying lens or microscope. It is composed of a mix of plagioclase feldspar, pyroxene, biotite, amphibole, and olivine (see green zone in chart below) making it dark in color and MAFIC (containing iron and magnesium).

Vesicular basalt is simply basalt containing small pockets or vessicles formed as gases escaped from the cooling magma.

Diabase, made of the same minerals, straddles the line between intrusive and extrusive. It's texture is somewhat more coarse than that of basalt.

Gabbro too is made of the same mix of minerals but because it is intrusive and formed slowly deep in the earth, it has larger crystals (1 to 10 mm) and has a coarse texture.

Basalt	Vesicular Basalt	Diabase	Gabbro

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