I asked around a couple of times about it but everyone said they had no use yet.
This may be true, but after reading up a little in the crafters corner on the gpotato luna forum i did found out there use or else there will be use.
read the following quote
Mysterious Powder, Oil, Fairy Tears, Moonlight Crystal, Dragon Bone Fragment,
Rune-Engraved Powder, Legendary Powder, Cruciate Powder
Mysterious Powder x1 + Oil x1 -> Magic Powder
Magic Powder x2 -> Spirit Powder
Fairy Tears x1 + Magic Powder x2 -> Fairy Dust
Moonlight Crystal x1 + Spirit Powder x2 -> Moonlight Essence
Dragon Bone Fragment x1 + Fairy Dust x2 -> Dragon Essence
Rune-Engraved Powder x2 + Dragon Essence x1 -> Rune-Engraved Essence
Legendary Powder x5 + Rune-Engraved Essence x1 -> Legendary Essence
Cruciate Powder x7 + Legendary Essence x1 -> Cruciate Essence
Dragone Bone Fragment (this will be Dragon Bone Piece if u ask me) together with 2 fairy dust (which u can make from 2 magic powders and those very rare tears of spirit) makes 1 dragon essence.
So anyways dragon bone pieces are used if i understand it correct for the next levels of
crafting rings, earrings and necklaces. So if u don't have reds. Or just like to keep boosting
your magic defense. Keep collecting those dragon bone pieces u'll need them later.
I'll test tonight if u can craft dragon essence already