My first is in graceful but not in gruel;
My second is in crystal but not in cruel;
My third is in trusted and also in truth;
My fourth is in yellow but not in youth;
My fifth is in ladle but not in lure;
My sixth is in perish and also in pure;
My seventh is boding but not in bed;
My eighth is in hinder but not in head.
I sit on the flagstones of MNI

Almost hidden from view--what am I?

10 points for first correct answer.
Ty, Chloee.