sentences: class is a property of a rock and includes values of sedimentary / metamorphic / igneous
docs: estate is class. phaeophyceae is class. slate is metamorphic_rock. market is class. metamorphic_rock is rock. metamorphic_rock is stone. marlite is metamorphic_rock. basalt is igneous_rock. igneous_rock is rock. shale is sedimentary_rock.