A sand ceremony is the same concept as lighting a unity candle. The bride and groom each get their own canister or vase of sand and at a specified time during the wedding ceremony, they will simultaneously pour their individual containers of sand into one. This symbolizes their separate lives becoming one. I have seen where 2 different colors of sand are used and the couple takes turns layering them into the shared container. This symbolizes that while their lives have become one, they are still their own individuals.
Thanks for the info. That sounds lovely!