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Gabbro, a coarse-grained, intrusive igneous rock is the most abundant gemstone material in the deep oceanic crust. Gabbro is composed mainly of calcium-rich plagioclase feldspar (usually Labradorite or Bytownite), Pyroxenes (usually Augite), and Olivine might also be present. This mineral composition usually gives gabbro a black to very dark green color. A minor amount of light-colored mineral grains may also be present in this beautiful gemstone from the deep ocean.
Gabbro can be found within thick lava flows of basaltic composition on Continents where slow cooling allows large crystal formation. Gabbro is present in the deep plutons formed when magma chambers feed basaltic eruptions. Large volumes of Gabbro are present beneath the Columbia River flood basalts of Washington and Oregon and the Deccan Traps of India.