Each of the following statements describes one or more characteristics of a particular metamorphic rock. Name the rock for each statement, then rank them from low-grade to high-grade.
(a) Foliated rock, sometimes derived from granite,
(b) Foliated rock, possessing excellent rock cleavage; generally used in making blackboards,
(c) Foliated rock containing about 50% platy minerals; named according to the major minerals in the rock.