Hah, Keirro and Shushi said what I was going to say already. XD
On the Diamond Fragments thing... there has been a 'Shattered Diamond' concept here in the quest forum for quite some time, but... there's also the matter that you can cut diamonds with other diamonds, so a diamond that's just been broken apart doesn't quite cut it (lawl) since it's possible that it could have been struck by another one. XD
It feels to me like you may be trying to make them seem more fel-essencey by adding extra random features onto them with the eerie glow and discordant sound statements. While those can be fine and dandy in moderation, it's also important for them to be able to stand on their own as good fel essences without those extras. An good example of this is Eirdirsceol's Unwithering Leaf essence, which had a curious red splatter on it but it's main feature was being fresh and green despite being detached from its tree for so long.
If you haven't already, check out other journals and quest threads to see what's been done, etc, etc, get a better feel of things and so on. XD
From the information you have on your quest thread so far, I feel safe in guessing you would prefer a precious metal or mineral involved in your fel essence, and some kind of aggressive or dangerous animal involved in your soul. ouo Have you thought about reptiles, by any chance? Maybe a
death adder in place of a deathstalker? :V Or if you want to stick to the arthropods,
this is a superb resource for animals with exoskeletons.
Silver that never tarnishes has a bit of potential, IMHO, and I'll have to disagree with Shushi about needing to add extra features, since staying pure and not-rusty is the unusual thing it's capable of in the first place. Maybe focus on a little bit of backstory to instill more curiosity in it, like how it ended up where it was before it was found by Kyou. It might also be worth keeping in mind that silver
isn't smooth and polished before it's mined and handled by humans.
