ABSTRACT
Gneisses are generally poorly foliated, medium-to coarse-grained feldspathic rocks. As such, they plot close to the feldspar corner of mineral proportion space: too much amphibole and they tend to be called amphibolite, too much quartz and they become quartzite, and too much mica and they become schist, for example. The poor foliation of gneiss is typically a consequence of having only small proportions of sheet silicates like muscovite and biotite, rather than from lack of strong deformation.
