A gabbro of the OceanicCrust

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The basic magma produced at the oceanic ridge slowly cools and crystallises as a gabbro (point 1 of the Path). This one is essentially bi-mineral: pyroxene is dark and the plagioclase is white. The rectangular shape of the latter is clearly visible ...

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...on the microphotograph. Under crossed-polarised light, pyroxene is yellow and the plagioclase, white to black, shows polysynthetic macles (=bands). Note the absence of a preferred orientation of the crystals, characteristic of a magmatic rock. Equilibrium exists between the two minerals, as evidenced by the contacts between them.

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