Amethyst has a Trigonal crystal system and is in the mineral class of oxides, the quartz group. It belongs to the group of crystal quartz that form large, visible crystals. It’s beautiful color comes from the traces of iron that are lodged between the layers of its structure.
Amethyst is formed hydrothermally, mainly in hollows that have been formed by gas bubbles in volcanic rock. It is also formed more rarely in rock clefts and rocks with channels running through them. A hollow that is lined on the inside with Amethyst crystals is called an Amethyst Druse (which is large) or an Amethyst geode (which is small).