This rainbow arch block set (comes with two) is perfect for adding style to any mantel, dresser, or desk or for using as book ends. NOTE: The size of each of these is 2.3" L by 4.75 H. W1.5" While they are sturdy and heavy, they will not hold up many large heavy books. These are gypsum cement and there are slight color variations that appear in the final product. Materials: These are handmade with gypsum cement, an eco-friendly sealer, and rubber pads. Gypsum cement is similar to Jesmonite, or eco-resin and is smooth, hard, and a strong surface with high water absorption resistance. Dry, the strength of our material is 10,000 psi in comparison to most concretes which vary from 2500-4000 psi. Imagine the durability of this stone is much like that of your favorite ceramic mug.