Iskallium Ore is an item added by HermitQuest. It is used to summon the Hermit Iskall85.
Iskallium Ore can spawn only below level y=12 in the overworld, and always appears as a single block. It is incredibly rare and hard to find. It can also break down nearby blocks (in a 5x5 cube), so may be found with sand, gravel, cobblestone or air blocks around it. When breaking down blocks, a 'rock crack' sound can be heard.