I have a friend-of-a-friend who reported being at the actual top-secret Rainbow Calsilica mine in Mexico. For those of you who wonder if the stone is fake, I can say that this guy saw the people actually removing it from the earth. So it is not man-made. He has a theory as to what creates the wild colors. He said that the mine is near a river, and upstream is the location of an ancient pottery manufacturing site. He theorizes that the colors from the pottery flowed downstream and leached into the soil, coloring the rocks in brilliant stripes. So the rock actually comes out of the ground, but its coloration might be due to humans of thousands of years gone by.