Historically Crystals have been divided in to Semiprecious and Precious classes.
Amethyst was found as precious class crystal, it was valued as Diamond, Rubin and Sapphires. But later on, was discovered large reserves of Amethyst in Brazil, which reduced its value.
Thru ages, all cultures saw crystals, as very strong energetic power and the one who carried crystals, contained the power of nature. Each crystal represented its own unique power.