Tridacna shell (Tridacnidae spp.) has a pattern on it that looks like the rut that a tire makes on a muddy road on a rainy day, so it’s called a Chequ shell in China. Tridacna shells are the whitest material in the world, with a thick, yellow-brown outer shell and a white and smooth inner shell. Tridacna shells are the largest shellfish in the deep sea. They are about a meter in diameter. In ancient times, people used one of these shells as a bath tub for their babies. Tridacna shells are a rare organic gemstone and Chinese Buddhist halidom. In China, they are also respected as the seven treasures of Buddhism, along with gold, silver, coloured glaze, agate, coral and pearl. Some Tridacna shells produce pearls. The peal was used as the top bead on a hat of an official’s rank sixth in power in the Qing Dynasty of China.