Infinity Stones (or Infinity Gems, in the comics) are primordial objects imbued with the powers of the universe. In James Gunn's Guardians of the Galaxy, the Collector (played by Benicio del Toro) describes them, saying, "Before Creation itself, there were six singularities. Then the universe exploded into existence, and the remnants of these systems were forged into concentrated ingots — Infinity Stones."
Thus far, five of the six Infinity Stones have been identified or recovered in the MCU: Space Stone (Tesseract, from Captain America: The First Avenger), Mind Stone (Loki's scepter, from The Avengers), Reality Stone (Aether, from Thor: The Dark World), Power Stone (Orb, from Guardians of the Galaxy), and Time Stone (Eye of Agamotto, from Doctor Strange). The sixth, the Soul Stone, has yet to be identified. But the question is, shouldn't Loki's Scepter house the Soul Stone, not the Mind Stone?
In The Avengers, Loki places his Scepter on people's chests, near their hearts, in order to control and manipulate them — nowhere near their minds. And when he tries do the same to Tony, nothing happens, because Tony's arc reactor is covering his heart. Furthermore, in Avengers: Age of Ultron, Vision is created by Tony uploading his A.I., J.A.R.V.I.S., into a synthetic android created by Ultron, augmented by the Mind Stone. But, in actuality, doesn't the Infinity Stone provide Vision with a soul, since J.A.R.V.I.S. already acts as the mind?