Xu Qingtong immediately grew interested upon hearing Xizi's words. "Oh? What sort of unusual mineral vein?"
Xizi emerged from underground, rolling two large eyes. "I don't know either. It just feels a little unusual, different from the mineral veins I've seen before!"
"Xiao Qi, do you know of any mineral veins that produce heavy concentrations of yin nether qi?" Xu Qingtong sent Xiao Qi a strand of divine thought.
Xiao Qi flew out of the Seven-Star Bracelet. Light flashed in those twin pupils as Xiao Qi looked underground. A moment later, Xiao Qi said, "Master, this is a nether vein!"
"What is a nether vein?"
"A nether vein is a very unusual kind of mineral vein. Its vein structure is fine, yet it can stretch for a thousand li. Wherever its veins reach, they can draw in the nearby yin baleful spirit qi, which ultimately gathers here. No wonder the yin qi here is so dense!" Xiao Qi said.
After pondering for a long while, Xu Qingtong took out the Little Four Symbols Formation and set it up around the cave. Hua Wuhui had probably excavated this place to collect yin nether qi.
If someone with ulterior intentions discovered such a place, another evil cultivator would inevitably arise. It was better to conceal it with a formation!
Xu Qingtong sat down on the meditation cushion, took out the Yin Nether Soul Refining Art, and studied it again. He had no intention of practicing such an evil art, but not practicing it would not prevent him from studying some of its subtleties. How to absorb yin qi, how to refine it, and how to reverse yin and yang, for instance, all had their merits.
At the thought of reversing yin and yang, puzzlement suddenly appeared on Xu Qingtong's face. He had