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.

Answer and Explanation:

The name of the rock for each of the given statements is given below:

(a) Gneiss is the the foliated metamorphic rock that has been derived from granite.

(b) Schist is another foliated metamorphic rock with excellent rock cleavage and is used in making blackboards in general.

(c) Slate is yet another metamorphic rock with 50% of platy minerals and and is named according to major mineral composition of the rock.

All of these are foliated metamorphic rocks with banded or layered look that is the result of pressure directed on it and heat exposure