Name the rock for each statement, then rank them from low 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.

Why might a single rock layer exhibit different types of sedimentary rocks within it? view available hint(s) why might a single rock layer exhibit different types of sedimentary rocks within it? such a rock layer, termed a facies, when traced laterally represents a variety of depositional environments that formed in a sequence over time. such a rock layer, termed a facies, when traced laterally represents a single depositional environment that formed over time. such a rock layer, termed a facies, when traced vertically represents a variety of depositional environments that formed at the same time across a broad area. such a rock layer, termed a facies, when traced laterally represents a variety of depositional environments that formed at the same time across a broad area. such a rock layer, termed a facies, when traced vertically represents a variety of depositional environments that formed in a sequence over time.