Eclogite

Eclogite is a dense, high-pressure metamorphic rock that forms from basalt or gabbro under extreme pressure and temperature conditions deep within the Earth's crust and mantle. It is primarily composed of red to pink garnet (pyrope-almandine) and green omphacite (a type of pyroxene), giving it a striking appearance. Unlike other metamorphic rocks, eclogite lacks plagioclase feldspar, which becomes unstable at the high pressures where eclogite forms. These conditions typically occur at depths of 40–60 km or more, such as in subduction zones where oceanic crust is forced into the mantle. Eclogite plays a crucial role in understanding geodynamic processes, as it is often associated with deep subduction and the recycling of oceanic crust. The transformation of basalt into eclogite increases rock density, which helps drive the subducting slab deeper into the mantle, influencing the movement of tectonic plates. Some eclogites are brought back to the surface through exhumation processes, often found in mountain belts such as the Alps, Norway, and China. Eclogite is also significant in mantle studies because some samples, known as "mantle eclogites," originate from depths of over 150 km and are brought to the surface by volcanic eruptions, particularly in kimberlite pipes that also contain diamonds. This suggests that eclogite can play a role in diamond formation, as carbon-rich fluids crystallize under high pressure. In summary, eclogite is an important rock in geology due to its role in plate tectonics, deep Earth processes, and even diamond formation. Its distinctive mineral composition and formation under extreme conditions make it a key subject of study in metamorphic petrology and geodynamics.