Amethyst is a type of quartz that often forms in geodes. Geodes are formed when lava hardens quickly (usually near Earth’s surface) and hollow cavities are formed from trapped gases. Once the outer layer of a cavity is hardened, silica-rich liquid must fill the cavity for crystals to form. Amethyst’s purple hue can be attributed to the presence of iron during the mineral’s growth. Every amethyst crystal should, ideally, have six sides with a pyramidal shape at the top.

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