Thirstystone 4 pack Black Natural Terrazzo Round Coasters. Terrazzo is a composite material made from chips of marble, quartz and granite that is held together with resin. Terrazzo coasters are a durable and stylish option for protecting your furniture. The unique material gives them a varied and eye-catching appearance, while their heat and moisture-resistant properties make them a practical choice for everyday use. Coasters measure 4.75" diameter.