Stoneline Group SL32-D-A-104-30-30 12" x 24" Walnut Travertine Bullnose Tumbled Coping 1.25" 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.