Soulstone
From Diablo Wiki
The Soulstones are a type of magical artifact which are used to contain the souls of very powerful beings. There were only three Soulstones in existence. Two of them were destroyed in Diablo II, what happened to the third one is yet unknown.
[edit] History
The Soulstones were created under the orders of the Archangel Tyrael in order to contain the spirits of the three Prime Evils when they were exiled into Sanctuary. It is speculated that the Soulstones were created from the much larger Worldstone, which helped suppress the powers of the Human race.
Tyrael ordered the creation of three different coloured Soulstones, each suited for the Prime Evil it contained-
The Soulstones were given to the Horadrim, who were eventually successful in capturing and imprisoning all three of the Prime Evils.
But what even the High Heavens did not know was that the Soulstones were the centerpiece of a diabolical plan by the Prime Evils in order to make way for the invasion of Sanctuary. The Prime Evils were told by Izual that they could use the power of the Soulstones to tap into the fiery energies of the Burning Hells while they were in Sanctuary. According to their plan, they orchestrated their own exile into Sanctuary and used their powers to corrupt the very Soulstones that held their essence.
The first one to take control of his Soulstone was Mephisto, the Lord of Hatred. He spread his influence across the higher ranks of the Zakarum priesthood and corrupted the surrounding lands of Kurast.
The second to awaken was Diablo, the Lord of Terror. It is possible that he was awakened indirectly by Mephisto; the Archbishop Lazarus was a high priest of Zakarum, and may have been already corrupted when he entered King Leoric's service.
Baal was not as lucky as the other two because of the method of his capture. Baal had, in his fervour, shattered his Soulstone and its biggest fragment was not enough to contain the demon. Tal Rasha, an exceptionally powerful Horadric mage, selflessly volunteered to act as an extension of the fractured Soulstone. So that Baal might not break free even after corrupting Tal Rasha, he was tied to a binding stone to wrestle the soul of Baal for all eternity.
After Diablo had freed himself, Marius, accompanied by the Dark Wanderer, pulled the Soulstone from Tal Rasha's chest, freeing Baal.
At the end of Diablo II, it is seen that Diablo and Mephisto's Soulstones were destroyed at the Hellforge and Baal retrieves his Soulstone from Marius. What happened to Baal's Soulstone after that is yet unknown.
[edit] Game
Mephisto's Soulstone is a drop from Mephisto which the player needs for the quest, The Hellforge in Act IV. It is not a problem, though, if the player forgets to pick it up, since Deckard Cain give them one if they enter Act IV without it.
Upon destroying the Soulstone, the player gets a Rune and some flawless or perfect Gems.
