The Norn Stones are enchanted stones belonging to Karnilla; they are often used in schemes by Loki, and were later used by Sif. Loki explains that the effect of the stones vary from person to person, depending on whether the stones accept the user and what they desire. Norman Osborn was unable to use, move, or affect the stones in any way.
Following the Hood's depowerment, Loki presents him the Norn Stones to grant him back the use of his powers. Loki later reclaimed the stones during the Siege of Asgard to give the Avengers a fighting chance against the Void, by using the stones to temporarily boost their powers. Unfortunately, the Void realized his enemies' source of power and killed Loki.
At some point when the stones were in the possession of the Hood, they were stolen by Mike Murdock, a human fragment brought into existence on accident through the power of Reader. Using a book of Asgardian spells he had hired Black Cat to steal, he used the stones to rewrite history and make himself a real person.
Ultimate Universe (Earth-1610)
In this reality, the Norn Stones are made of the same substance as Mjolnir, and are the "avatars of power" for Asgard. There are 24 sacred runes that, when placed in proper sequence in an access portal in northern Germany, allow gates to open to seven accessible realms, as well as a "room with no walls". Loki used the stones to launch a massive invasion of Earth through Central Park.
Avengers: Earth's Mightiest Heroes (Earth-8096)
In this reality, the Norn Stones were set of nine powerful magical artifacts created by Karnilla, the Norn Queen. Amora the Enchantress and Baron Zemo planned to use the Norn Stones to concur Earth. Zemo sent his Masters of Evil to specific locations across the global to open portals to the Nine Realms. With the Norn Stones, Zemo was able to scatter the Avengers to different realms.