Menachite Forerunner crystal

The Forerunner Crystal, referred to by the Covenant as the Fragment of Divinity, the Shard of the Gods, or the Holy Light, was a Forerunner artifact that was discovered in the underground Menachite Forerunner Complex on Reach by Dr. Catherine Elizabeth Halsey and the surviving Spartan members of Red Team in 2552. The artifact is of incredible potential, capable of warping space, energy, gravity, and even time and Slipspace. It is hardly understood by the UNSC forces who found it, but is a prize that the Covenant were extremely eager to obtain.

Bubble Effect
When it enters Slipspace, the Crystal begins emitting radiation that causes a ship to move hundreds of times faster than it would during normal Slipspace travel. The realm that it opens is not normal Slipspace, which is a non-visible lack of space, but rather an anomalous bubble region of blue mist. Also in contrast to "normal" Slipspace is the allowance of weapons fire - not possible within regular Slipspace. Energy weapons will be horribly misdirected and will pop in and out of existence seemingly randomly, causing them to be just as dangerous to the firer as it is to the target. However, the extreme strength of the radiation makes it impractical for the UNSC to carry the crystal through Slipspace for a prolonged period of time; it would kill the crew in under seventy-two hours, even if shielded.

Description
The Forerunner artifact is a fist-sized crystal with a thousand facets that is tapered at both ends and glows with a blue light. When originally seen by Dr. Halsey and the SPARTANs in the underground facility, it was floating upright and the area around it was distorted by gravity. The crystal reacted with a burst of neutron radiation at Halsey's touch. When exposed to a Covenant gravity beam, the crystal nullified it, reshaping itself in the process. Its new form was created as the top half split along its facets and opened like a flower blossom. The petals undulated, and the crystal's glow changed from sapphire to a cool green. When Ascendant Justice jumped into slipspace it rearranged itself into a starburst of edges and refracted light, emitting radiation even after it was stored in the Pelican's reactor compartment.

Appearance
When the Ascendant Justice jumped into Slipspace, the crystal again rearranged itself, emitting radiation during the entire jump, and caused gravitational distortions. The location of the ship at the end of this jump was somewhere near the Eridanus System, a distance that, from Reach, should have taken several days to traverse instead of a few minutes. By comparing timestamps from several missions Dr. Halsey discovered a three-week average time difference. Her conclusion was that the Crystal bent both space and time, so that it could be removed from Reach by Cortana and the Master Chief. Halsey later gave the crystal to Corporal Locklear, who covered it with C-7 Foaming Explosive and destroyed it to avoid another Slipspace radiation spike, killing himself in the process.

Three shards of the crystal were recovered by the Covenant, which were presented to the Prophet of Truth by Tartarus in an orb-shaped container. Truth then ordered the Brute to reward the pilots that had recovered the shards, then kill them. The UNSC also possesses pieces of the crystal. It is unknown what has happened to the shards that were possessed by the two factions, although the three Covenant-recovered shards were likely lost when High Charity fell to the Flood invasion, or were kept aboard the Dreadnought with Truth.

The rift that was projected when the ship went into slipspace may be similar to the Portal found at Earth. It is probable that the Forerunners used this crystal, or others like it, to travel throughout the galaxy and past its edge almost instantaneously.

Trivia

 * At the end of the novel Halo: First Strike, Truth is given three chips from the crystal. He then says it "may yet be enough for our purposes". The exact implication is open to speculation; he may simply have hoped to harness its effects as a weapon.
 * The amount of radiation it produces in Slipspace is too great to be contained. In Halo: First Strike, the Master Chief puts it inside a Pelican's reactor, but the radiation leaked didn't noticeably diminish.
 * The crystal occasionally releases a large number of neutrinos, an unknown type of them, possibly a 4th generation or higher lepton.