Sterling Silver Marcasite and White Agate Rectangle Ring The natural properties and composition of mined gemstones define the unique beauty of each piece. The image may show slight differences to the actual stone in color and texture. Gemstones may have been treated to improve their appearance or durability and may require special care. The natural properties and composition of mined gemstones define the unique beauty of each piece. The image may show slight differences to the actual stone in color and texture.