Looking through this specimen of calcite will have you seeing double. The unique crystal structure of calcite allows it to split and transmit a beam of light into two, displaying two of the same image - this is especially fun to do with a laser pointer. Each specimen exhibits calcite's characteristic rhombohedral cleavage, making it a comprehensive tool for geology classrooms. This sample of calcite is between 2 and 2.5 inches long, and weighs between 2 and 4 ounces. Samples vary naturally, and may not look identical to those pictured. If you reach out to us before you buy, we will send a picture to ensure you are receiving a specimen you'll like.