Must Zakah be paid on diamonds etc.?

Praise be to Allah, the Lord of the World; and blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

No!, Zakah should not be paid on diamonds unless they are meant for trade. If diamonds used as trading goods reach the Nisaab (minimum amount liable for Zakah) by themselves or when added to some other goods, then their Zakah should be paid.
Allah knows best.