Black and white represent Yin and Yang, which describes how seemingly opposite or contrary forces may actually be complementary and interdependent in the natural world and how they may give rise to each other as they interrelate to one another. Curve lines represent Water in Wu Xing. Obsidian, attributing to Water, white crystal, attributing to Metal and tiger-eye attributing to Earth, interpret the relationship of mutual generation and mutual overcoming between Metal, Earth and Water.