My sincerest apologies towards my fellow users who professed that Loki's scepter was an Infinity Stone. I didn't want to believe it for two reasons. First, I didn't think Thanos would be foolish enough to entrust an Infinity Stone to someone like Loki. Secondly, the scepter's gem had a blue glow to it. Soul Gem is green while the time gem is orange which would make the Mind Gem yellow. If the scepter's jewel glowed bright yellow then that would have put my speculations to rest.

However, this raises another question. Loki's scepter was originally used as a divining rod to find the Tessaract and it was used to disrupt the gateway that the Tessaract had opened. Could it be that the gems can repel or deflect one another's power? Can this be an advantage for the Avengers when they face Thanos?

As a side note, I think using Loki's staff as the Mind Gem is a cheat. I think the Mind Gem could have been utilized somewhere else and could have made a bigger impact. All that's left now is the Soul Gem and Time Gem. It seems pretty clear that the Soul Gem will make its debut in Dr. Strange with Adam Warlock and the Time Gem will be needed to reverse the devastation of Ragnarok.