Answer:
Diamond is pure carbon, C
Zircona is zirconium oxide,

Step-by-step explanation:
Chemical symbols are used to distinguish one atom (or molecule) from the other.
Diamond is composed of pure carbon (C) where each C atom is bonded to four other C atoms forming a repeating network of tetrahedrally linked C atoms. Therefore, the chemical symbol of diamond is C.
If the chemical symbol of zircona were also 'C' then it would prove that both are identical. However, zircona is essentially zirconium oxide which has a chemical formula,
. Therefore, the different symbols suggest that the two are not identical.