The spectrum of ways quartz can form and its ubiquitous presence in the Earth’s crust have led to dozens of common names for one simple mineral. They can get tricky to keep straight, so it helps to understand the logic behind them. First, consider varieties of quartz as falling into two basic categories. Crystalline quartz occurs in a range of colors, each bearing its own common name. Purple crystals are amethyst, while those ranging from yellow to orange are known as citrine. Quartz specimens with crystal structures too hard to see without a microscope fall under the generalized name of chalcedony. Opaque specimens of chalcedony are called jasper. Agate is translucent chalcedony and often exhibits a layered pattern. Unfortunately, people don’t always apply these names consistently. Jasper is often confused for agate, and vice versa. Varieties of quartz also share names with other minerals, like topaz. Knowing the basics can help make navigating the maze of quartz’s common names a little easier.