Amethyst: The very first protective crystal in the list is the amethyst, a purple variety of quartz also renowned as the birthstone for February. Since folklore, it is believed to protect & shield people from negative energies & toxic environments. In ancient Greek, amethyst was assumed to help individuals prevent intoxication and keep them quick-witted. In Medieval Europe, soldiers too wore amethyst in the form of amulets in battle to protect themselves and keep their heads cool.