Final answer:
The growth of highly equant crystals does not contribute to the formation of foliation in metamorphic rock. Foliation is primarily caused by rotation of platy and elongate minerals, application of differential stress, crystal deformation, and recrystallization.
Step-by-step explanation:
The growth of highly equant crystals (i.e. crystals whose dimensions are about equal in all directions) does not contribute to the formation of foliation in metamorphic rock.
Foliation in metamorphic rock is primarily caused by the rotation of platy and elongate minerals, the application of differential stress, crystal deformation, and recrystallization.
Rotation of platy and elongate minerals, such as micas and amphiboles, causes the minerals to align parallel to each other, creating a layered appearance. Application of differential stress causes minerals to align perpendicular to the direction of stress, enhancing the foliation. Crystal deformation occurs when minerals undergo plastic deformation, resulting in elongation or flattening. Recrystallization is the process where crystals dissolve in one direction but grow in another, leading to the development of new minerals with preferred orientation.