After Thor: The Dark World, it was ultimately confirmed we were heading toward the Infinity Gaunlet storyline. We also knew that the Tesseract and the Aether are both Infinity Gems. Then Guardians of the Galaxy arrived in theaters and it was reaffirmed that the Infinity Gems were indeed being introduced throught the MCU:
1. James Gunn and Kevin Feige have both confirmed that the Orb in Guardians was in Power Gem. It, however, was purple and not red like its comic book counterpart. Kevin Feige has come out on numerous occasions and said the Gems would not match up with their comic sevles. Much speculation has gone into which Gems are which.
2. After careful consideration, I believe that the Tesseract is indeed the Space Gem. It opened a wormhole to the other end of space to allow Loki and the Chitari to come through to Earth.
3. The Aether was a bit tougher to decide, at first I believed it was the Power Gem. After rewatching Thor: TDW about ten times since its Blu-Ray Release (and some online studying) I noticed that the Aether acts for itself. The Asgardians also refer to it as a singlar entity. During my research, the Reality Gem is thought to be most unstable and seeks out a host. In Thor: TDW the Aether seeked out Malekith and eventually Jane. The entire plot to the movie was about breaking down the walls of reality with the Aether, so it has to be the Reality Gem.
That would make Three Gems clearly identified and spread out across the MCU with the Collector given the Aether(Reality), Asgard protecting the Tesseract( Space), and the Nova Corps protecting the Orb (Power). That would leave us earthlings with nothing to protect, that is where my theory comes into play. What if Loki's Scepter is indeed the Mind Gem?
1 Let us start with the obvious, at the beginning of The Avengers, Loki took control of Hawkeye and Dr. Selvig's mind with his scepter. That is the most basic function of the Mind Gem.
2. Later on in the film, Loki uses it to transport his mind to the Sancatury for a meeting with The Other. He refences that someone put the scepter in Loki's hands. The quote went "You dare question him? He, who put the scepter in your hand." Another function of the Mind Gem is that it can munipulate ones dreams as well as their thoughts. Who is to say Thanos wouldn't give Loki his one and only Infinity Gem in hopes of him bringing back a second in the Tesseract( Space)? The entire plot of Loki's scheme was to retrieve the Tesseract and use it to bring the Chitari to earth. Once Loki had become King of Midgard, he would give The Other and eventually Thanos the Space Gem. He would probably need to give the scepter back as well, but we never found out because Loki lost, but more on that later.
3.(& 4.) On two occasions the scepter manipulates minds of the Avengers. The obvious was Hawkeye and Selvig. Hawkeye even mentions to Widow that it felt like he had his mind plucked out and something else put back in. This was obviously the control from the Mind Gem. How do you think Hawkeye found the Hellicarrier? The Gem lead him to it. The the other occasion is a little more subtle. As the Avengers are beginning to fight just before Hawkeye blows up the engine on the Hellicarrier, Bruce is seen holding the scepter as he is yelling at Fury. My theory is that the Loki and the Mind Gem were manipulating Bruce to Hulk out, which he eventually did. This would give reason for why he had control the second time he Hulked out in the final act, but not the first time. At the end of the movie, we do not see what happened to the scepter as the last person to have it was the Widow, so it is implied it is with SHIELD.
5. That is case until the Captian America: The Winter Soldier. Hydra has infiltrated SHIELD at its highest level and has full and complete control. This includes everything in their position including Loki's scepter, which is confirmed to be in Baron Von Struckers' position in the post credits teaser. Joss Whedon, Kevin Feige and Aaron Taylor Johnson have confirmed that Wanda and Pietro Maximoff volunteer for these Hydra experiments. This leads me to believe they are using the scepter to manipulate abilites. In my research, I found that the Mind Gem can increase mental abilities in the form of Psoinic powers. Guess who has telekenetic powers? The Scarlet Witch does. They could take a few liberties with the Gem to also give super human speed but is that a coincidence or what? If and when Von Strucker uses the scepter to give Pietro and Wanda abilties, this should all but confirm this is indeed the Mind Gem. This would also give way to my next point to about Loki and his scheme impersonating Odin.
There are two major theories out there, one where Loki is still working for Thanos as he impersonates Odin or the one I believe which is Loki lost the battle of New York and is Running scared. At the end of the Avengers, he was all too eager to give up and turn himself into the Avengers. " I'll have that drink now"......He lost to the Avengers and Thanos is pissed. He was perfectly happy in prison hiding from Thanos, before Thor broke him out. Loki , then, fakes his own death and is now impersonating Odin. This is all one big scheme to make sure Thanos thinks he is dead until there is a time he can make amends to Thanos for having lost the battle at New York. Thanos has clearly moved on to and from Ronan in his search for the Gems. If the scepter is the Mind Gem and Loki lost both it and Tesseract. Loki would need to make up for it in a big way, maybe....THE GAUNLET AND TESSERACT(space), which are both safely in the vault in Asgard. Again this is all just speculation, but is truly interesting, isn't it? Can't wait to see what clues Avengers Age of Ultron gives us....Give me your thoughts in the comments below....THANKS (Sorry tried to embedd images but I suck at it)