Amethyst is, in essence, a purple variety of quartz. It becomes purple due to irradiation and in iron impurities in the crystal, and in some cases other transition metals.
This is one of the most famous and widespread stones out there. Before the 18th centrum, it was considered one of the most valuable stones. It was referred to as “A cardinal gem” along with Rubies, Safire’s, and Emeralds. It was also explicitly referred to in Buddhist text as the birthstone for people born in February, the stone was considered sacred and often turned into prayer beads.