Sigil Stone (Skyrim)

Sigil Stones are magical objects that open portals between Nirn and Oblivion. The Sigil Stone is a necessary ingredient for the forging of Daedric armor and Daedra hearts at the Atronach Forge in The Midden beneath The College of Winterhold.

Acquisition
To obtain a Sigil Stone, the Dragonborn (after reaching a Conjuration level of 90 or higher) must seek out Phinis Gestor, a Master Conjurer of The College of Winterhold. Phinis provides them with a summoning spell that calls forth an Unbound Dremora. Heading to the roof of the Hall of Attainment, the Dragonborn needs to cast the spell in a circle of candles. After defeating the Dremora, the Dragonborn demands that the Dremora return to Oblivion and brings back a Sigil Stone. He obliges, thus giving the Dragonborn a Sigil Stone. In exchange for the Sigil Stone, Phinis Gestor teaches the Dragonborn Flame Thrall, as well as now offering to sell other Master level Conjuration spells. The Sigil Stone will be returned to you after learning the new spell.

Quests

 * Conjuration Ritual Spell

Bugs

 * Sometimes the Dremora becomes untargetable. This means he is unable to be un-summoned or killed, permanently disrupting the quest. The only known fix is to reload to before the quest and try again.
 * Sometimes the floor in the training part of the guild will be glitched open and a chest will have that and other valuables.
 * You can receive a second Sigil Stone. If you place the stone in the Atronach Forge right after initially receiving it and then talking to Phinis. He will take nothing out of your inventory but return another Sigil Stone when completing the quest. The second Sigil Stone is effectively useless though.
 * If the dialogue before fighting the Dremora is skipped he can't be summoned again.
 * The Dremora will sometimes reappear after the quest is completed, and be untargetable. however, if you order a follower to attack, the dremora will agro on you. This is highly discouraged as neither you or your follower can deal damage to the dremora, however he can damage you. Also, the dremora is nearly impossible to evade.
 * The Sigil Stone can also be found in a secret chest in the college of Winterhold. You can get to it by doing the out of the map glitch. This secret chest is located in the Hall of the Elements in the outside ring when you do the glitch. To get inside the chest you have to jump and while you are falling you have click the chest, look inside it and then fall but you shall be teleported back to the position that you jumped from with all the obtained items from the chest in you inventory.