Amethyst

Amethyst was a fancy stone related to agates and other varieties of quartz but held a higher value. The deep purple hued stones were sometimes called "the crown of kings" because many rulers tried to decree that they only be used by royalty. Among the drow, worshipers of Ghaunadaur knew these gems were sacred to their deity for consecration or sacrifice, and they were sometimes sent by him to show favor or disfavor, depending on the circumstances.

Description
Gem quality amethysts could be a light to deep purple, with the deep "royal" hues fetching the highest prices. Amethysts were usually facet cut to show off their brilliance. A typical specimen had a base value of 100 gp.

Powers
Amethyst was one of the "nine secrets" used in the creation of ioun stones. This stone could also be used in the casting of spells that facilitated communication, such as magic mouth. Powdered and used in magic ink, it was used to make scrolls of these same spells. The best time of day to use amethyst as a component or ingredient was at mornbright.

An amethyst was a required material component in casting swordward, a Tormish spell. Crushed amethyst was also a spell component required for casting Nezram's amethyst aura.

If a being wore enough amethyst gems of the highest quality, they conferred an unnaturally high degree of resistance to spells that attacked the mind, including complete immunity to chaos, feeblemind, hold monster, magic jar, and quest.

Rumors & Legends
Folktales said that this stone could prevent intoxication and neutralize poisons so they were frequently used to decorate the drinking vessels of the nobility. In reality, they had no such abilities. It was said that if amethysts appeared in a woman's dream, it represented romance. In the language of oracles and seers, amethyst represented safety.

Legends say that the original Amethyst was a young and beautiful priestess's name. She was favored by Sune and Selune. The goddesses fought over the priestess eventually destroying her. A glance from Selune turned the priestess into moonlight and the spilled wine from the goddesses' feast table gave Amethyst her purple hue.

Another rumor of amethysts' magical properties was its ability to drive away malicious oni.

Trivia

 * Priests of Shar generally liked to wear jewelry including amethysts when it was practical to do so.
 * In the church of Torm, amethyst was the color (for robes or dyed armor) worn by priests with the high rank of Vanguardier.
 * Amethyst was considered a prized stone among the drow. They preferred ones of darker hue more than those of lighter ones.