Types of Quartz: The Complete Variety Guide

Quartz is silicon dioxide, written SiO₂, a framework of silicon and oxygen atoms locked in a rigid lattice. That structure gives every variety the same core properties no matter what it is called or what color it shows.

Three traits do most of the identifying work. Quartz sits at 7 on the Mohs hardness scale, hard enough to scratch glass and steel. It has no cleavage, so it does not split along flat planes the way calcite or feldspar do. Instead it breaks with a conchoidal fracture, the smooth curved shell-like surface you also see in flint and glass. It is also fairly light for a mineral, with a specific gravity near 2.65, and it leaves no streak on a porcelain tile.

Hold those four facts together, hardness 7, no cleavage, conchoidal fracture and a glassy luster, and you have the signature that runs through every entry below. The varieties differ in appearance; the mineral does not.

For the full mineral data, the Quartz reference on Mindat lists every documented property and locality.

Macrocrystalline quartz forms crystals you can see, often as six-sided prisms ending in a point. The colors come almost entirely from trace impurities and natural radiation acting on the silica, which is why one mineral produces purple, yellow, pink, gray and clear stones. These are the varieties most people picture when they hear the word crystal.

Chalcedony is quartz built from crystals so small they cannot be resolved by eye, sometimes called cryptocrystalline or microcrystalline quartz. Because the grains are tiny and tightly packed, these stones look waxy or glassy rather than crystalline, take a high polish, and come in solid colors, bands and patterns instead of distinct points. They formed from silica-rich water seeping into cavities and cracks, often layer by layer.

Chalcedony itself is the umbrella term and also the name for the plain, translucent gray-to-blue or white material. The well-known stones below are all members of the family.

Two materials fool people most often: glass and calcite. The properties from the first section settle both cases quickly.

Glass mimics clear and colored quartz, especially in tumbled stones and beads. The fastest tells are temperature and bubbles. Quartz is dense and pulls heat from your skin, so it feels cold and warms slowly; glass warms fast in the hand. Hold the piece to a bright light and look for trapped round bubbles, a dead giveaway for poured glass, since natural quartz inclusions are angular or needle-like, never neat spheres. Hardness confirms it: quartz at 7 scratches glass, and glass near 5.5 cannot scratch quartz.

Calcite is the classic mineral mix-up, because clear calcite and clear quartz can look alike on a shelf. Two properties separate them cleanly. Calcite is much softer, at 3 on the Mohs scale, so a steel knife or even a copper coin marks it while quartz is untouched. Calcite also has perfect cleavage and splits into neat rhombs with flat faces, whereas quartz has no cleavage and breaks with a curved conchoidal fracture. A drop of vinegar fizzes on calcite and does nothing on quartz.

When a photo is all you have, an AI crystal identifier reads the color, luster and crystal form and flags likely look-alikes, which points you to the right physical test instead of a guess. Confirm anything valuable with a hardness or fracture check in person, since a picture cannot measure either.

Quartz is common, so most varieties are affordable, and that is part of the appeal. Clear, milky and smoky quartz are inexpensive even in large pieces. Amethyst and citrine carry a modest premium for strong, even color, and deep-purple amethyst from a few classic localities fetches the most among the everyday types.

A few things lift price beyond the variety itself. Rutilated quartz with fine, well-arranged golden needles is sought after. Natural untreated citrine commands more than the heated kind once it is verified. Among chalcedony, fine agate, vivid carnelian and well-patterned jasper are valued for the pattern and polish rather than rarity of the mineral.

Treatment matters more than name. Heated amethyst sold as citrine, dyed agate and irradiated prasiolite are still real quartz, but they should be priced and disclosed as treated. The stone is genuine; the only issue is a seller who hides the enhancement. For the wider context on quartz varieties and their naming, the Quartz entry on Wikipedia is a solid reference. If you want to see how the named varieties fit into the bigger picture, our guide to the types of crystals groups them alongside the other mineral families.