The specimen pictured here is a rare form of bladder stone known as a jackstone.
This variety is referred to as a “jack” stone because of its resemblance to the metal objects in the children’s game, Jacks. Jackstones occur most often in the urinary bladder and less frequently in the upper urinary tract. These stones are often composed of calcium oxalate, and they form in the crevices and trabeculations of the urinary bladder. As they grow, new minerals deposit on the irregular shape, forming larger and larger spicules.
Photo credit: Figure 1 Medical Images
To see more cases like this, visit Figure 1.