Polarized light micrograph of phaneritic (coarse-grained) gabbro microcrystals (thin section). It is very variable in mineralogy and composition: plagioclase feldspar, pyroxene (clinopyroxene and orthopyroxene) and smaller amounts of olivine, biotite, amphibole, and others. Gabbro is a mafic (rich in magnesium an iron), intrusive (magma cooled slowly in the crust) igneous rock, the plutonic equivalent of basalt an diabase. It is an essential part of the oceanic crust (mid-ocean ridges) and very abundant on Earth and the Moon. It often contains valuable amounts of nickel, chromium and platinum. Uses: construction, roading industries, and ornamental (known as "black granite"). Field of view size: 528 x 791 痠 (0.021 x 0.031 in)