Jen's Herald

Thor 3 will introduce the Soul Stone i believe, the 6th and final Infinity Stone. The Soul Stone is on the chest plate of Heimdel the Asgard Gatekeeper. there is an orange glow above the Tree of Life etching on his chest plate, and the Soul Stone is orange in color in the comics. Heimdel also says in the first film, that he 'can see 10 trillion souls', hence the stone is part of his power.

Thanos needs all six Infinity Stones for his universe-destroying Infinity Gauntlet. the first five stones are already in play in the MCU.

Stone 1 is the Tessaract from Captain America and Avengers. it is now in the possession of Loki, who is posing as Odin on Asgard. (blue stone is also known as the Space Stone)

Stone 2 is the Aether from Thor 2, it is now in the possession of the Collector who is in the employ of Thanos. (red stone is also known as the Reality Stone)

Stone 3 is the Orb from Guardians of the Galaxy. it is now in the custody of the NOVA Corps on Xander. (purple stone is also known as the Power Stone)

Stone 4 is the control source of Loki's sceptre from Avengers 1 and 2. it is now in the forehead of Vision, of the Avengers. (yellow stone is also known as the Mind Stone)

Stone 5 is the Eye of Agamoto from Dr Strange, and is in the chest plate of Dr Strange's costume. (green stone is also known as the Time Stone)

God help the universe if Thanos ever gets hold of all six stones! :/