Travertine Rock, 3pc, aprox. 3x2x2 inches each Travertine is a form of limestone. It is a calcium carbonate precipitate. This type of rock forms in and around mineral springs. As the minerals are deposited organisms grow between the layers. Eventually the organisms die and pores and gaps are left leaving a lightweight porous material. This rock is great for bonsai with its light color contrast and because of it's porosity moss and algae grow in the pores and cracks. This material is rare and hard to find. Photo does not do this rock justice, it is covered in nooks and pores! Limited!