Assertion: slate | /r/HasProperty | a type of rock
Facets:
Source sentences:
text: Slate is a type of rock which has been used on floors and roofs for hundreds of years.
text: Slate is a type of stone; you can identify most slate roofs by the way the light hits it from a certain angle.
text: Slate is a type of rock, and offers excellent strength and durability as a roofing material.