This pelite (garnet staurolite schist) is from within the staurolite zone of the Connemara Dalradian Supergroup. The staurolite crystals commonly grow transverse to the schistosity, and so grew after it had developed. The garnet, in contrast, is augened by the schistosity, and so grew earlier. Crenulations may appear in quartz inclusion trails within the garnet porphyroblasts, showing that two phases of deformation had occurred before the garnet grew.
The Dalradian rocks of Connemara lie to the south of the Highland Boundary Fault (which crosses Ireland from Fair Head to Clew Bay), so it appears that late faulting shunted the Connemara terrain southwards from its original position (north of the HBF) to its present location.
(Thin section is contaminated with carborundum)
Rotation 1 - Three nice staurolite crystals, with good yellow pleochroism. Biotite and muscovite.
Rotation 2 - Muscovite deformed around garnet.
Rotation 3 - Augened garnet in muscovite and biotite, and ‘late’ staurolite pleochroic, tiny tourmaline.