Thirstystone Round Natural Black Marble Coaster 4 Pack. Thirstystone Natural Marble Coasters have an elegant and luxurious look. Each Coaster is made from Natural Marble and has its own unique pattern. Marble is durable, heat tolerant, and protects your surfaces from scratches, stains, and water rings. Each Coaster measures 4.5” diameter. Marble can easily be cleaned with a damp cloth or sponge making a low maintenance option.