Wraithbone is the primary construction material used by the Eldar, and the staple of their psycho-technical engineering. It is a form of crystallized psychic energy that can exist as a solid in realspace brought forth from the Warp and shaped by an Eldar concentrating his thoughts and intent upon it. All Eldars are able to influence Wraithbone to a certain extent; for instance, most Eldars walking the Path of the Artisan will use Wraithbone in order to create the pieces of art or instruments they desire. However, truely complex constructions (such as functional weapons or whole voidships) can only be brought into existence by the Eldar Bonesingers; those specialised craftsmen who focus on understanding and mastering the intricacies of creating, growing and shaping the Wraithbone through the application of their innate psychic power.
When and where the Eldar first began using Wraithbone is unknown, though most Imperial scholars assume it was in the distant past, long before humanity had even fully evolved to sentience. It is used to create the Craftworlds of the Eldar, all of their edifices, their tanks and other vehicles, robotic constructs such as the Wraithguard and Wraithlords, as well as their individual weapons and armour. It is a psychic conductor and thus provides not only the structure and armour for the things built of it, but also the power distribution and communications systems since Wraithbone carries psychic energy the way a wire or fiber optic cable carries electricity or photons. Wraithbone can also naturally generate a psychic shield that protects the occupants of any spacecraft made from the material from the predations of the entities of the Warp, much like an Imperial Gellar Field. It was this psychic shielding property of Wraithbone that protected the souls of the inhabitants of the Craftworlds from the birth of the Chaos God Slaanesh which destroyed so much of the Eldar race.
Wraithbone is a psycho-plastic material that is highly resilient to damage, and capable of limited self-repair. It, and the other building materials of the Eldar, will grow and react more like living tissue than the building materials of other races, save for the Tyranids' bio-constructs and Necrodermis, the Necron living metal that is the basis of a majority of the Necron's technology. Wraithbone provides the psychic structure that allows it to become a repository for the spirit of a dead Eldar hero. An Eldar spirit is drawn from the Infinity Circuit of a Craftworld and resides within a Spirit Stone mounted in the construct until such time as its power begins to fade and it can no longer function.
- Codex: Craftworld Eldar (3rd Edition), pg. 5
- Codex: Eldar (4th Edition), pg. 13
- Path of the Seer (Novel) by Gavin Thorpe