Why use turtle shells instead of other substances as divination tools?

Divination with tortoise shells, divination with tortoise shells and copper coins. Prepare a turtle shell and some ancient copper coins. The ancients thought that the tortoise's back armor was as bulging as the sky, its belly armor was as flat as the ground, and the tortoise seemed to carry heaven and earth. Therefore, the tortoise is regarded as a spirit that can know astronomy in the world and geography in the world. Its shell is used to predict the rise and fall of life and as a mascot to predict bad luck. During the Yin and Shang Dynasties, the diviners of the emperors barbecued tortoise shells with charcoal fire, and according to the cracks on the tortoise shells, they divined for the emperors and predicted state affairs, wars, weather and disasters. The origin of the word "Bu" is that after the turtle shell is burned, cracks similar to "Bu" are easy to appear, and these cracks are used to predict fate. According to legend, the pattern of gossip is also inspired by the tortoise shell pattern of tortoise.

The custom of divination with tortoise shells has spread to this day, and many numerologists still use tortoise shells and copper coins to tell their fortune. Fortune telling is forbidden to kill animals, especially turtles regarded as psychic by China people. As a result, many people replaced real turtle shells with copper turtles and wooden turtles. In particular, most of the native turtles in Taiwan Province Province are endangered, and their shells are not easy to obtain, and most of them have been included in the conservation category, so they cannot be captured and slaughtered.