Li Shizhen explains, “Renpo is found in the soil under a person who has hanged himself or herself. It resembles soft charcoal. If the Renpo is not dug out in time, it will penetrate deep into the earth where it cannot be traced.”[14] The Bencao gangmu compares a hanged person’s soul with similar phenomena, “When a star descends to the earth it turns into a stone. When a tiger dies, his eyesight descends and turns into a white stone. Human blood will turn into phosphorus or jade when it drops to the ground.”

-from “Traditional Chinese medicines derived from the human body” wiki