Plangent crystal

Plangent crystal was a magically animated mineral mined in Durpar. It was used by the Datharathi in the construction of prostheses. It was purple, lavender, or puce in hue; the Datharati claimed prosthetics built from it were better than the original limb, and they also controlled all access to it.

History
Plangent crystal, also known as Datharati crystal, was actually a form of matter found in the Celestial Nadir, known to Ususi Manaallin and the Deep Imaskari as Celestial Nadir crystal. Ususi Manaallin's keystone for accessing the Celestial Nadir was made from this crystal.

Around, plangent crystal was mined exclusively from under Adama's Tooth. The first prototype of plangent was Warian Datharathi, who had an arm created by Shaddon Datharathi, his grandfather, after he lost his own in an accident. Only five years after that, plangents were common in the city of Vaelan and all but two members of the family, Eined and Zeltaebar Datharati, had replaced at least some parts of their bodies with crystal in order to show they stood behind their work. Among the products sold, the enhancements were named "Strong and Tireless", "Quick and Vigorous", "Insightful and Spellstrong", "Pious and Healing", and "Cerebral and Ki-Strong". A whole-body prosthetic was available, with all the enhancements in it, though it was extraordinarily expensive.

Unknown to everyone but Shaddon himself, the crystal was not actually mined from Adama's Tooth, but from the Celestial Nadir, accessible through a portal. The vein he had used for Warian's prosthetic was abandoned once he found a purer vein. From this vein, he had been able to improve on his prosthetics to the point of making them better than normal limbs, and also gained the power to control and spy on all plangents. Unfortunately, the source of power for all those improved plangents had turned out to be sentient: an Elder Evil known as Pandorym, who was in turn capable of controlling Shaddon after the latter replaced most of his body with plangent crystal. Only Warian's prototype arm, fashioned from lesser crystal, was still immune to both his grandfather's control and Pandorym's. The superior crystal was likely acquired from close to the place where Pandorym's body was stored.

Shaddon Datharati also created several spiders made entirely out of crystal. Several creatures throughout Vaelan had been embedded with fragments of the crystal, putting them under Pandorym's control. Monsters in the Imperial Weapons Cache were also embedded with, or carried, plangent crystal. During its battle with Ususi's party in the Cache, Pandorym made use of several Deep Imaskari who were under the crystal's influence as well.

By, the local practice became known all around Faerûn as not only replacing a limb, but also enhancing the plangents' talents in a minor way. By, the crystal was mined from several quarries under Datharati control; presumably all of them were connected to the Celestial Nadir in some way. Even within the merchant house, how to find and mine it was a tightly guarded secret.

Rumors
It was said that Curna emeralds might have had traces of plangent crystal in them.