The Silver-Clad Crystal Shard are quest items which can be used to increase the amount of Fervour replenished by flasks.
Lore
My chest was pierced by a strong guilt, and I heard the voice of the Miracle. A voice that needed no words, nor sounds, to be understood. The voice spoke of a penance that would grow my body into a great statue. That would empty my insides leaving only the bones, enveloped in scarlet velvet. That would unfold my skin, as if it was a blessed mantle, revealing the hollow skeleton below.