Originally Posted by cherokeesam
So you're saying the Mind Stone is already somewhere here on Earth? If it's powered *by* the Mind Stone, then the Mind Stone must have been nearby for Loki to use it in the Avengers and for it to be used again in the near future. Seems pretty far-fetched, but can you think of anything that hints at the Mind Stone's existence on Earth in the Avengers movies?
Not exactly. Again, this is complete speculation...
When I said the scepter might be powered by the Mind Stone, I don't mean it needs to be in direct contact or in proximity to the Mind Stone. I'm assuming Infinity Stone technology to be slightly more advanced than our smart-phones.
What I'm suggesting is that the Mind Stone is what gave the scepter it's mind-altering properties when the latter was constructed (possibly by Thanos). Like a one time "power up" kind of deal. Not dissimilar to how the WW2 HYDRA weapons were "powered" by the Tesseract.
So, Fury might have based his "powered by the Tesseract" comment on the fact that the energy signature was the same. However, the hypothetical Mind Stone, like the Tesseract is an Infinity Stone and thus might have similar properties.
This solves a couple of problems:
1. Since the scepter is not the Mind Stone itself, Thanos would have no problem giving it to Loki.
2. I believe Feige confirmed the Tesseract to be the Space Stone. It would make more sense for the scepter to get its mind-altering properties from the Mind Stone rather than the Space Stone.
Then again, it would be slightly simpler from a storytelling perspective to just go the "yes, the scepter is (and/or contains) the Mind Stone and Thanos knows he can retrieve it whenever he chooses" route.