Sea green jade was produced from the natal qi of a high-grade spirit vein, along with the energy of Dao evolution present in that qi as the vein grew closer to evolving into a lesser dragon vein.
Those conditions were what made it so rare. If someone absorbed even a single wisp, the sea green jade would never form, because the natal qi of that spirit vein disappears upon any absorption taking place within its grounds, no matter how small.
Then there was also the fact that even if all conditions were met, there was a chance it would not form, since, as with most things in life, a little bit of luck and timing was also needed.
