[Where is the charizardite Y?]

37 minutes ago, Rendolf said:

I believe you receive it at the end of the Murmina Sidequest, which is started by going to the room accessed by repairing the Calcenon staircase, but she only appears after the Battle of Agate.

no, that's charizardite x. I need charizardite y.

[Where is the charizardite Y?]

I just can't find the damned thing. Anyone know where it is?