Espers turn into magicite upon their death. Possessing magicite allows ordinary humans to learn magic. Kefka gains the power to crystallize live espers, its animation resembling the spell Banish. Espers can also crystallize into magicite at will without being on the brink of death.
Lifestream can crystallize into Materia. Usually this takes a long time, but the process can be expedited by Mako Reactors. Crystallized Lifestream has magical properties and allows the wielder to cast spells, among having other effects. Dummied text from the game suggests that summoned monsters are great spirits that crystallized themselves into Materia.
After falling into the Lifestream, Sephiroth becomes crystallized deep in the Northern Cave. He remains there acting through a shapeshifted Jenova. When Rufus Shinra and the other executives of the Shinra Electric Power Company discover the Northern Cave where Sephiroth remains, they find it covered in crystallized Lifestream: Materia, and deduce it to be the fabled Promised Land.
Sephiroth's biological mother, Lucrecia Crescent, is crystallized within a solidified Lifestream fountain in a remote cave east of Nibelheim. She has sealed herself away due to being unable to kill herself and feeling she is unfit to reside with the rest of humanity. It is stated in the Dirge of Cerberus -Final Fantasy VII- Official Complete Guide by Scenario Coordinator Hiroki Chiba and Producer Yoshinori Kitase that Lucrecia is still alive, that the crystal she resides in is a product of Lucrecia herself, and that her imprisonment within it is self-imposed.
Pyreflies can crystallize into spheres by reacting to people's feelings and memories and binding them with images and audio. Spheres make use of these properties of pyreflies to make recordings. The raw material for spheres is water that contains a high concentration of pyreflies, gathered from specific locations, such as the Macalania springs.
When a l'Cie, a human branded by a fal'Cie, has completed their Focus, they will turn into a crystal. The appearance of a l'Cie's crystal varies depending on the type of fal'Cie that brands them. Most have their bodies naked and transparent, surrounded by additional crystal pillars, but some l'Cie retain their original appearance (and clothing), and one is seen frozen inside a large crystal. If a l'Cie fails their Focus they turn into a crystalline monster known as a Cie'th. Cie'th can eventually petrify into Cie'th Stones with the l'Cie's crystal embedded in it.
Lake Bresha is crystallized when the Pulse Vestige housing the fal'Cie Anima falls into it. The water turned to crystal, the party can cross it on foot. When Cocoon falls from the sky, Ragnarok erects a crystal pillar to support the now-crystallized shell of Cocoon above Gran Pulse.
Monsters have a chance of turning into a crystal when defeated in battle. This allows them to be used as Paradigm Pack allies and develop them through the Crystarium. People's memories can also crystallize into crystals known as fragments, found throughout the timeline.
After Gran Pulse merges with Valhalla, a crystallized Lightning sits on the goddess Etro's throne. According to a Datalog entry and the "Requiem of the Goddess" downloadable episode, Lightning crystallized herself after accepting defeat in her battle against her rival, Caius Ballad.
After Lightning and the combined souls of humanity fell Bhunivelze, he turns into a colossal crystal before being sucked into the new unseen realm. The party wonders if he is really dead or merely sleeping, but Lightning is convinced humanity would persevere again should he ever return.
Crystallization sometimes occurs during heavy concentrations of aether. The most dramatic case occurred after the Battle of Silvertear Skies, in which the landscape surrounding Lake Silvertear underwent mass crystallization due to the dying wyrmking's life force mixing with ceruleum leaks, creating a barren landscape unlike any other.
Crystallization also occurred to the fragments of Bahamut after the Battle of Carteneau, and the floating landmasses above Abalathia's Spine often exhibit evidence of crystallization at the bottom. In Final Fantasy XIV: Shadowbringers, the Crystal Exarch's body has partially crystallized due to having fused with the Crystal Tower.
Crystallization is related to the battle system. If a unit remains knocked out for three turns (determined by the unit's Speed), their body will perish and become either a crystal or treasure chest; if said unit is undead, it has a chance of reviving with a random amount of HP instead.
Once a unit becomes a crystal, any units who claims the crystal can either learn the abilities of the dead unit, or fully recover their own HP and MP. The downside about learning the abilities is that the unit who claims the crystal has to have the job class available. If the player picks an ability from a crystal, all listed abilities will be learned. Any treasure chests found will contain an item the deceased unit had equipped.
The crystals of defeated human units are based on their color palette. The party and guests (palette 00) have the teal-gray crystal, the Order of the Northern Sky units (palette 01) have the bright blue crystal, the Order of the Southern Sky units (palette 02) have the red crystal, the Corpse Brigade/Baert Trading Company/random battle units (palette 03) have the yellow crystal, and the Church of Glabados units (palette 04) have the purplish-gray crystal.
The world of Orience is governed by the four Crystals of Orience who are sentient beings able to brand l'Cie to carry out their Will. Those the Crystal deems successful become sublimated and turn into crystal. This also crystallizes the sublimated l'Cie's final thoughts into a crystal shard known as a l'Cie Stone. During the First Battle of Judecca the Azure Dragon Crystal Primus l'Cie Soryu crystallizes the clouds with its breath.
High Commander Jegran of the Royal Army is revealed to be a Crystal Bearer with the power of crystallization. Upon touching someone with his right hand, if he so wills it, the person or creature will be crystallized, transforming into red crystals in the shape of the living being it once was. Said crystals are easily shattered, and are said by Amidatelion to be one of the elements disrupting the Crystal Principle.
Jegran once planned to crystallize every member of the Selkie Guild so they could serve as fuel to the crystal reactor of the battleship Alexis, but his plans were crushed by the efforts of Layle, Amidatelion, Keiss, Belle and Vaigali.
Crystallization is the (natural or artificial) process of formation of solid crystals precipitating from a solution, melt or more rarely deposited directly from a gas.