JEAN-CLAUDE REVY, ISM / SCIENCE PHOTO LIBRARY JEAN-CLAUDE REVY, ISM / SCIENCE PHOTO LIBRARY
Metagabbro rock sample. This is a metamorphic form of gabbro. Metamorphic rocks are formed when heat and pressure in the Earth's crust alter the structure of existing rocks, in this case gabbro. Gabbro is a very common igneous rock. It is formed when molten magma rises upwards through the Earth's crust, and forms much of the oceanic crust. The additional metamorphic processes that formed the metagabbro have also formed the mineral glaucophane, which gives this sample a blue-grey colour.
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