Liked it as well as the previous one. It was nice to see more about the new Ghost Quartz (or, should I say, Cairngorm) and her interactions with Phos, who desperately tries to act more cheerful, compared to the previous depressed self.
Sensei's relation with the Lunarians is starting to slowly reveals itself. After Phos and Cairngorm return from a serious fight with the Lunarians, they present to him the only thing they managed to get from them: a polished board. Sensei acts like they doesn't recognize it, but when they leave, they recall the days they play with it.
Speaking of the Lunarians, they are starting to become much more of a serious threat. At one battle, they sent little gem bugs-like things, which manage to steal fragments from the other gems. And, at the last battle, Phos lost their head and they had it replaced by Lapis Lazuli's head (Lapis Lazuli was Ghost Quartz's previous partner, before being captured by the Lunarians. Only their head was saved).
Again, like in the previous volume, I couldn't understand what was going on, due to the mangaka's art style. If there's even gonna be a second season, I hope they fix this problem.
Moving on to Vol.7!