In the photograph below, under crossed polarizers, an extinct garnet grain in a schist contains numerous quartz inclusions.
Garnet is isotropic, therefore extinct under crossed polarizers. In thin section, it may be colorless, pale red to dark brown, greenish, etc. All members of the garnet family have very high relief, and they commonly form euhedral crystals.
The photograph above left shows garnet under uncrossed polarizers; chlorite is altering the garnet along its left margin and within a fracture. The photo on the right with crossed polarizers shows a garnet crystal at extinction, surrounded by muscovite and glaucophane in glaucophane schist.
Garnet is characteristic of metamorphic rocks such as schists, but it may also be found less commonly in igneous rocks.
In the photograph below, under crossed polarizers, an extinct garnet grain in a schist contains numerous quartz inclusions.