Thirstystone Rainbow Sandstone Coaster 4 Pack. Sandstone coasters are a popular choice for their natural and earthy look. Sandstone coasters are made from natural sandstone, which is a sedimentary rock composed of sand-sized minerals or rock grains. Sandstone is a sustainable and environmentally friendly material. Sandstone has a unique pattern of grains and colors, which makes each coaster a one-of-a-kind piece. Sandstone is naturally absorbent. These Sandstone Coasters will continually absorb condensation from beverages. Sandstone is also heat tolerant, making it a great choice for protecting tables and countertops from hot beverages. Each coaster measures 4” x 4” square. Sandstone coasters are easy to clean with a damp cloth or sponge.