Can't tell your Mind Stone from your Reality Stone? You're not alone. Those Infinity Stones are a tricky business.

They keep popping up in the Marvel Cinematic Universe. Thanos wants to assemble them. The Tesseract in The Avengers was one, as was the crystal in Loki's staff, which played a big part in Age of Ultron. The Aether from Thor: The Dark World was another, and so was the orb that everyone wanted in Guardians of the Galaxy. That's four down; two others are still unaccounted for.

So which gemstones are which?

Today Marvel made things a little easier for fans by posting online an eight-minute feature that will also be included on the Avengers: Age of Ultron home video release. It's the perfect time to catalog the stones, because the next time the Avengers are seen fully assembled on screen (not counting Captain America: Civil War, because Hulk isn't in that one) will be Avengers: Infinity War, Part 1 in 2018.

That's when big villain Thanos is expected to assemble the stones into the all-powerful weapon known as the Infinity Gauntlet.

Ready to learn more? Watch "Infinity Six," Marvel's new feature. It's embedded below.

So when do you think we'll see the Time Stone and the Soul Stone? There are plenty of opportunities, with five flicks scheduled between now and the first Infinity War film. The Soul Stone seems like something that could show up in the Doctor Strange movie. The Time Stone? That's anybody's guess.

Avengers: Infinity War, Part 1 will be in theaters on May 4, 2018. Avengers: Infinity War, Part 2 follows a year later, on May 3, 2019. Captain America: The Winter Soldier and Captain America: Civil War directors Anthony and Joe Russo will direct.

h/t Comic Book Movie

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