Stone rings have also been found at Nok Culture sites. They are normally found as fragments but can be identified as rings because of their flat, oval or triangular cross-sections and their shapes. These stone rings are very rare and their purpose is unknown. Another rare find is stone beads, which are typically found as if strung on strings. Beads tend to be carefully made out of hard siliceous rock such as quartz, chalcedony, jasper, or carnelian. There are three different bead shapes: cylindrical, which is the most common shape, as well as rod and ring-shaped.