HP-LT Metapelites

In High Pressure - Low Temperature metamorphism, the metapelites only exceptionally contain Biotite. The mica is white and it is the phengite ; Chlorite can be added. Garnet is not rare, quartz is abundant...

The black chloritoid tablets should not be confused with biotite!

Below is a microphotograph of the typical paragenesis of these rocks:

Sometimes, if the composition of the protolith allows it (if the rock contains plagioclase for example), the micaschist can contain a lavender blue amphibole, Glaucophane (Glc) and Epidote (Ep) (or Lawsonite depending on PT conditions). Quartz is rare in this photo of a thin section in Pane Polarised light.