Amethyst is a violet variety of quartz.
The name comes from the Koine Greek ἀμέθυστος amethystos from ἀ- a-, “not” and μεθύσκω methysko / μεθύω methyo, “intoxicate”, a reference to the belief that the stone protected its owner from drunkenness.
The ancient Greeks wore amethyst and carved drinking vessels from it in the belief that it would prevent intoxication.
Amethyst is a semiprecious stone often used in jewellery and is the traditional birthstone for February.
The picture is one of my privately owned amethyst and it was gifted to me quite some time ago.