Is there a symbol for the 90th anniversary?

Traditional anniversary symbols are based on years married and typically only go up to 75 (most people don't live long enough to be married longer). I was interested in this question since the choral society I belong to will be celebrating its 90th anniversary. I did find a couple references on the web that 90 was diamond and emerald (but listed as a modern symbol, not traditional). For a wedding anniversary gift you could go with jewelry with diamonds and emeralds in it. For an anniversary symbol for our choral society celebration I will probably suggest "Double Sapphire" since sapphire is for 45 years (2 times 45).