We think of the "white stones" more as a prophecy that we feel was fulfilled.. but around the Shrine of Baha'u'llah which is at Bahji near Akko the walkways are full of round white stones which are from the Sea of Galilee.
Thanks all. I am sure other groups put their symbols on gem stones as well. I heard from a Kurdish Baha'i that the Bab used to hand out white stones. I had a dream about a rock and "coincidently" saw it later that day of the dream and then was given one by the owner. The rock is a jasper conglomerate. Jasper apparently represents the oneness of mankind according to AbdulBaha.