Assertion: metal's form | /r/MadeOf | 12 and 106.7 atoms
Facets:
value: in the rhombohedral unit cell
type: LOCATION
value: respectively
type: MANNER
Source sentences:
text: Crystalline boron is a very hard, black material with a high melting point and exists in many polymorphs: Two rhombohedral forms, α-boron and β-boron containing 12 and 106.7 atoms in the rhombohedral unit cell respectively, and 50-atom tetragonal boron are the most common.