What is an eclogite in geology ?

Eclogite - Metamorphism

Metamorphic facies diagram
Eclogite is a rock of general metamorphism, massive and hard, very dense (3.5) with a greenish-black, dark green or green hue punctuated with red. Mineralogically it is composed of garnets (solid solution rich in pyrope) and pyroxenes (omphacite), with various accessory minerals, white micas (phengite, paragonite), kyanite, quartz, rutile, ilmenite, magnetite, etc...

Eclogites are rare rocks which form discontinuous bands in metamorphic regions, or constitute enclaves brought up by lava. The genesis of these rocks requires high pressures (13 to 15 kbar) and high temperatures (700 to 900°C) which implies formation at great depth, at the base of the crust or in the upper mantle (between 40 and 80 km). In France, eclogites are particularly abundant in Vendée (Massif Armoricain).