well, having made the game during the last days I can assure that byib.hrc is the 3d model that is used for the first materia found in the game and for the keystone. I have no idea why they use the same model for it's two objects especially since the first materia to find is a cure materia.
gwib.hrc is indeed the 3d model used for seto's tears when nanaki see his father statue.
And for the rest
ateb.hrc= yellow
aude.hrc= purple
awbe.hrc= red
ctbe.hrc= blue
dabf.hrc=green
hjdc.hrc= black