Assertion: slate | /r/HasProperty | rock
Facets:
value: in nature
type: LOCATION
value: essentially
type: DEGREE
Source sentences:
text: Slate is essentially a rock, a homogeneous metamorphic rock that is derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism.
text: So why would slate be chosen as a roofing material, when there are so many rocks in nature to pick from?