Infinity Stone

The Infinity Stones

SPOILER ALERT: This article includes multiple spoilers for the Marvel Cinematic Universe.

The Infinity Stones are powerful alien artifacts in the MCU. Six are known to exist. All contain or channel vast quantities of energy. They are inherently dangerous, and they will destroy most people who attempt to handle them directly. Technology can be used to harness their energy with much lower risk.

Origins

According to the Collector, the Infinity Stones are remnants of "singularities" that existed before the Big Bang. An ancient race of advanced aliens made them into artifacts of immense power. At least one of their uses was to cleanse planets of all life. These aliens appear to be the Celestials from the comics.

Known Infinity Stones

The Tesseract is a glowing blue cube that was hidden on Earth by the Asgardians sometime in Earths' past. It was discovered by Hydra leader Johann Schmidt and used to power an assortment of high-tech weapons during World War II. It was eventually dropped into the Atlantic Ocean and later recovered by SHIELD. Loki attempted to recover it for an alien benefactor in return for being made ruler of Earth, but his plan failed, and the Tesseract was taken back to Asgard. With the right technology, the full power of the Space Stone can be accessed, allowing the user to create wormholes through space that can be used for instant transit over interstellar distances.
The Aether is a reddish blob of fluid that Dark Elf leader Malekith sought to use to destroy the Nine Realms and return the universe to a state of complete darkness. He was defeated by Thor, and the Aether was taken to the Collector for safe-keeping. If the full power of the stone is accessible, the user can alter reality in arbitrary ways.
Ronan the Accuser, a Kree renegade, attempted to use an Infinity Stone (a glowing purple ellipsoid with no specific name given, called the "Orb" after its container) to destroy the planet Xandar. So far, it is the most dangerous to handle directly; one of the Collector's servants tried to use it, causing an immediate explosion that wrecked his museum. Ronan was able to hold it long enough to install it in his hammer, which allowed him to access some of its power safely. The Guardians were able to combine their wills to control it long enough to use its power to destroy Ronan. Following Ronan's defeat, it was put back in a container and stored in a vault in the Nova Corps headquarters on Xandar. This stone's only special property is generating vast quantities of power.
The stone in the sceptre given to Loki by Thanos incorporated the Mind Stone (no other name specified). It is known to contain an advanced artificial intelligence and to be able to create persistent AIs apart from itself. The stone has since been incorporated into an android body created by Ultron. As Thanos presumably would not relinquish control of the Mind Stone lightly, it must have been necessary to the process Loki used to transported himself to Earth, which involved remotely forcing the Space Stone to open a worm hole that he could use to get there.
The Eye of Agamotto in Doctor Strange is a device for containing and controlling the Time Stone. Using magic or technology, the stone can be used to change an objects place in time, restoring it to a previous state or advancing it to a later state.
The Soul Stone is stored in a shrine on the planet Vormir, and a mystical sacrifice is required to recover it. The special powers of the stone have not been revealed.

Control

As noted, it is dangerous for a living being to directly handle an Infinity Stone. However, their power can be safely channeled through technological instruments or magic rituals. Arnim Zola was able to use machinery to siphon energy from the Tesseract and store it in "batteries" for use in weapons and vehicles. Ronan was able to attach the "Orb" to his hammer and manipulate its power indirectly without being harmed. Thanos had a gauntlet constructed into which he could install the stones; this gauntlet resembles one stored in the Asgardian weapons vault.

Malekith was able to control the Aether using his mastery of Dark Elf magic. Likewise, Doctor Strange was able to use sorcery to utilize the power of the Eye of Agamotto.