Without flesh or bone to animate, crystalkin cannot be raised as normal undead such as skeletons or zombies. However, they are humanoids, and thus are not immune to necromancy. When a crystalkin's corpse is affected by necromantic magic such as animate dead, it rises as an undead crystalkin called a gravegem.

Gravegems resemble living crystalkin, except all color has drained from them, leaving them dull and gray. They usually have many cracks or fissures along their crystal body. Some parts may even be broken or fully shattered. Their bodies become brittle and fragile, sometimes even as brittle as a piece of chalk, and the resulting fractures make most gravegems sharp and jagged.

Soulless Puppets. Gravegems created by spells are generally obedient to the commands of their creator. A gravegem is not typically as obedient as a skeleton, but not for unruliness. Gravegems lack almost any impetus or will of their own, and must be given very specific and exacting instructions. Gravegems have little motivation, even when magically commanded by a controller. They almost never follow through with their assigned tasks to ensure they have been fully done, wandering off to fulfill their own whims at the first sign of success instead.

Empty Vessels. When uncontrolled, gravegems are possessed by a desperate hunger for identity. They can't recall even the slightest detail about their life, and they lack all personality beyond the most basic sense of self. As a result, an uncontrolled gravegem will wander aimlessly until it encounters signs of humanoids or even civilization. If it finds living humanoids, the gravegem will attack them, seeking instinctively to acquire their trappings of identity. Gravegems might wear clothing, jewelry, and even body parts from people they've killed.

Undead Nature. A gravegem does not require sleep.

Crystalkin are a race of humanoids found in the D&D Unleashed compendium The Elements & Beyond. They hail from beyond the Astral Plane, where they are born as fragments of the great Mother Crystal.

Crystalkin are called to travel the planes and discover their destiny, but extended time in certain planes might infuse their crystal lattice with different magic, severing their psychic connection with the Mother Crystal and changing the crystalkin's innate nature forever, and even altering them into a different type of creature entirely.

Crystal Nature. A crystalkin (of any kind) does not require air, food, or drink.