The Hemat Stone is a Unique Amulet in Diablo IV Season 15. It comes from Bartuc (Lair Boss loot table) - one guide S13 guide.
Unique power
Bonuses from Command Valloch and the Ritualist Shard and its Fragments have 200%[+] increased Potency. Your Occult Skills deal [40 - 60]%[x] increased damage.
Affixes
Willpower
Skill Ranks to Occult Skills
Where it drops
Bartuc (Lair Boss loot table) - one guide S13 guide