Assertion: metal's form | /r/HasProperty | black
Facets:
Source sentences:
text: The three allotropic forms of arsenic are yellow, black, and gray; the gray allotrope is the most common.
text: The most thermodynamically stable, and least reactive, form of phosphorus is black phosphorus, which exists as three crystalline (orthorhombic-, rhombohedral- and metallic, or cubic) and one amorphous, allotrope.