What are Precious Soul Fragments?

Get 50 Precious Soul Fragments and earn a Precious Soul that will give you either a Sacrificial Heart (worth anywhere from 600 to 4000 essence for sacrificing) or Gold Idol (worth anywhere from 50,000 to 1,000,000 gold when sold)

Precious Soul Fragments are earned by completing Skull Quests. You can also choose to convert any other type of Soul Fragment into a Precious Soul Fragment.