Assertion: hafnium | /r/HasProperty | to separate element
Facets:
value: because of their extreme chemical similarity
type: CAUSE
value: among the most difficult
type: OTHER
value: in the periodic table
type: LOCATION
Source sentences:
text: Zirconium and hafnium are among the most difficult to separate elements in the periodic table because of their extreme chemical similarity, due in part to so-called lanthanide contraction.