Zakaat on precious stones
There is no Zakaat on precious stones like diamonds, rubies, etc. even though they come under jewelry. No matter how high their value is. As mentioned in Fatawa A’alamgiri, Vol. 1, Pg. No. 180.
However, if these are bought and kept as trading goods, then Zakaat is Compulsory on them if they meet the prescribed criterion and 1 year passes on them.