What is the basalt in the basalt of Qinglong White Tiger Suzaku?

Xuanwu is a spiritual thing composed of turtles and snakes. Xuanwu originally meant Xuanming, and the ancient sounds of Wu and Ming are interlinked. Wu means black; Ghost means yin. At first, Xuan Ming described the turtle divination as follows: the turtle's back is black, and the turtle divination first invited the turtle to ask questions in the underworld, brought back the answers and showed them to the world in the form of divination. Therefore, the earliest basalt is the tortoise.