Amethyst gets its purplish color because of the presence of iron and other impurities in the gem, and their reaction to the gem's natural radioactivity. Amethyst is made out of quartz. Pure quartz is often clear and colorless.
Amethyst can also change its color in reaction to heat and light, and so a purple amethyst is best kept away from direct sunlight and high temperatures.
Amethyst is the birthstone for February. Its name comes from the Greeks and means "not intoxicated." The ancient Greeks believed that the stone could prevent a person from getting drunk and even carved drinking vessels out of the stone.