Fate Crystal

Fate Crystal is a mysterious substance known to grow on at least one Frozen Fate in the Frozen North. Proximity to it brings increasing degrees of sickness, madness, and physical corruption, but if refined it can form weapons sharp enough to cut through planes.

Properties
The crystals grow on and around an active stable Fate in the Frozen North. It is unclear whether the ability to generate these crystals is specific to this Fate or type of Fate, or whether it is a reaction to the extreme temperatures and particular magical environment of the Frozen North.

Proximity to a crystal causes increasing levels of mental agitation, distorted thought processes, and eventual physical growth of crystals out of organic and inorganic material. These effects are in addition to the madness effects of a standard active Fate, and persist even when the crystal is separated from the Fate. Excessive exposure can prove permanently maddening, disfiguring, and eventually fatal, even to non-living creatures such as constructs and undead.

Harvesting and refinement of the crystals is extremely difficult, as any equipment and/or personnel used to handle them will become crystal-corrupted; even golems appear to go mad from these effects, though more slowly than minded beings.

Crystals are sharp enough to cut holes between planes; the party has observed that the crystals may constantly be puncturing the space between planes, but at such a small level that the tiny rifts close themselves almost immediately. They are also extremely sharp when used in battle, ignoring armor and hardness. It is unclear whether the consciousness of the one known True Crystal Sword is a fluke or whether all madness crystals are sentient.

In Aegis
Fate Crystals are documented in several books currently held by Nara°i and found by Scarlet in a wizard's library on Sigil. The only known source on the prime is the active fate in the Frozen North.

The party encountered Touliang's refinement operation at his base in the Frozen North, though they did not explore the crystals themselves.

The only successful refinements of Fate Crystal witnessed by the party are the True Crystal Sword wielded by Trevor and the tiny pocketknife currently carried by Scarlet. These crystals do not emit the normal area effects, though the sword is intelligent and has merged with Trevor himself, and any long-term effects of exposure have not had time to manifest.