Quartzite is a metamorphic rock made almost entirely of the mineral quartz. Quartzite begins its geologic life as sand grains, perhaps on a beach, desert dune, or riverbed. Over time, the sand grains become compressed and stuck together to form sandstone. If the sandstone gets buried ever more deeply underneath layers of rocks, it gets hotter and more compressed. With enough heat and pressure, the sand grains lose their original shape and fuse to their neighbors, forming a dense, durable rock. The process is similar to individual snowflakes merging into solid, glacial ice.
Quartzite is usually white or light-colored because quartz sand is light colored. Additional minerals carried by groundwater can impart hues of green, blue, or ion-red. Van Gogh and Azul Macaubas quartzites are examples of vivid coloring.
Regardless of color, quartzite is made of one thing: quartz. That’s helpful because quartz has distinct properties that make it easy to tell apart from other minerals. (Note talking about the mineral quartz, not the composite countertop material that is also named quartz.)