Can a 9 carat wedding ring wear down an 18 carat engagement ring?

Q, Are the two stones of the same hardness

These are very large stones and to be of this size, for the most part would be of a softer Material, such Mho - scale hardness of 6.4 - 9. Opal - Emerald.

Answer to your Q, is judge only by the some material, Of said stones.

If the stones are different in material hardness there will be wear on stones.

Though most setting are of findings That well last a life time.

To save the stones of there original state, would be to keep the apart.