Fine-grained gneiss is a deep regional metamorphic rock with feldspar and quartz as the main minerals (generally between 50% and 90%) and dark minerals as the supplemental minerals (generally <30%). It has very fine grains, a homeo-granoblastic texture and a gneissose structure. It contains intermediate acidic plagioclase and microcline and forms by the alignment of flaky or columnar minerals such as biotite, hornblende, pyroxene, tremolite and magnetite. It is differentiated from other types of gneiss by its finer granularity, even mineral distribution and abundant light-coloured minerals. Fine-grained gneiss is a product of the migmatization of siltstone, tuff and intermediate acidic lava.