Sillimanite zone (Sample 8318)

The assemblage is Sil + Grt + Bt + Kfs + Pl + Qtz.
This sample comes from the contact aureole around one of the younger granites, rather than from the regional sillimanite zone, but it adequately represents a typical assemblage in the upper part of the amphibolite facies. Sillimanite is mostly of the fibrolitic variety, forming sheaves draped around the grain boundaries. Garnet forms rather small rounded crystals. Biotite occurs in red-brown, poorly-aligned flakes. Matrix quartz and plagioclase are granoblastic.

Field of view is 7 mm wide.