Slice of natural two-tone Agate from the state of Rio Grande do sul, Brazil, on an elegant black and satin brass display. And before it was that stone, it was an air bubble in the cool lava of a volcano. The lava became basalt: a porous rock, and this chamber was successively filled, over millennia, by water with dissolved minerals. Like Manganese oxide that gave these black lines all around. Each flood brought a different density and color layer... That is especially visible when light goes through it: the blue color becomes translucent and the heart of white crystals is highlighted (photo 4 ). And all this is perfectly natural.