Stoneline Group SL32-D-A-104-30-11 6" x 12" Walnut Travertine Bullnose Tumbled Coping 2" Thickness. The gorgeous auburn and beige tones of the Walnut collection blend perfectly with a wide variety of designs. These travertine stones are quarried in Turkey, a country well-known for producing high-quality natural stones. The warm tones of the Walnut collection provide excellent material to create a relaxing and inviting atmosphere to unwind at the end of a long day.