So, in another thread we are comparing the highstorms(body of honor) to the mists(body of preservation). I wonder if we could draw a similar parallel between atium(body of ruin) and gemhearts(body of cultivation).
We know that atium is caused by the physical body of the shard leaking into the physical realm and manifesting in solid form. Also, they fuel allomancy.
We've been told that the chasmfiends have a symbiotic relationship with some spren that allows them to grow to their enormous size. Perhaps that spren is feeding leaked cultivation essense into the gemheart and causing it to manifest and grow. We know that soulcasting consumes the stormlight, but perhaps there is a special power available that would consume the gem inself. Much like atium is only consumed if a specific power is used.