In this retrograde eclogite, garnet (red, Gt) and clinopyroxene (brown, Cpx) are no longer in equilibrium, as shown by the black corona around the garnet. Observation under the microscope shows that this rim consists of hornblende and plagioclase...
... and results from the destabilization of the Gt + Cpx assembly according to the reaction Gt + Cpx + Q = Hbl + Pl. (Observation in Plane Polarised Light)
...we observe the reaction Omphacite = Cpx + Albite (sodic Pl ).
When the mineral reactants of the reaction (Gt + Cpx) are entirely resorbed, , the rock becomes an amphibolite.
On the Path, these transformations are used to draw the arrow n°6.
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