Amethyst

Start with the obvious clue — a purple color in any shade from pale lilac to rich violet — and then confirm it is quartz. Well-formed amethyst grows as six-sided (hexagonal) prisms capped by a pointed, pyramid-shaped termination, the classic quartz crystal habit; in a geode you will see many of these points crowded together. The color is frequently zoned, stronger near the tips and patchy or banded within the crystal, which is exactly what natural amethyst should look like.

The hardness test is decisive. Quartz sits at 7 on the Mohs scale, so a genuine amethyst will scratch glass and a steel knife will not scratch it — a quick way to rule out softer purple stones and most glass imitations. Amethyst also has no cleavage: instead of splitting along flat planes, it breaks with a curved, shell-like conchoidal fracture, the same as clear quartz. Purple color plus a hexagonal crystal habit plus a hardness of 7 plus conchoidal fracture together confirm amethyst.

Amethyst spans a wide range of purples, from a faint, almost pinkish lilac to a saturated, inky violet. The deepest, most evenly colored material — sometimes marketed as "Deep Russian" — is the most prized, while paler, washed-out stones are far more common. Color zoning, where bands or patches of stronger purple sit within a paler crystal, is typical of natural growth and is not a flaw.

Two related quartz varieties are worth knowing. Prasiolite, a leek-green stone often sold as "green amethyst," is almost always produced by heat-treating natural amethyst, not by nature; it is real quartz, just artificially colored. Ametrine is a natural blend of amethyst and citrine in the same crystal, showing zones of purple and golden-yellow side by side. Both illustrate how closely amethyst, citrine and clear quartz are related — they are all the same mineral, differing mainly in trace impurities and heat history.

Amethyst carries a long cultural history as a stone of sobriety, calm and clear-headedness. The name itself comes from a Greek word meaning "not intoxicated," and the ancient Greeks and Romans associated the stone with protection against drunkenness — a tradition that survives today in amethyst's reputation as a calming, focusing and clarifying crystal. It has also long been linked with the so-called crown chakra and with meditation.

These associations are spiritual and cultural rather than medical. Amethyst is valued in many traditions for promoting a sense of calm and clarity, but it is not a treatment for any condition and should never replace professional medical or mental-health care. Enjoy it for its beauty and its history, and treat "healing" claims as matters of belief and personal meaning, not science.

Amethyst is abundant and, for most pieces, very affordable — tumbled stones, small points and geode slices are inexpensive, which is part of the stone's broad appeal. Because supply is plentiful, value is driven almost entirely by color quality: deep, even, richly saturated purple commands a clear premium, while pale, gray-tinged or unevenly colored material is cheap. Good clarity, a clean crystal shape and an attractive, fully crystallized geode also add to the price.

There are no fixed prices for amethyst — what a piece sells for depends on its color, size, clarity and form. As a rule of thumb, when comparing two pieces, the one with deeper and more uniform purple will be the more valuable, all else being equal. Large cathedral geodes and finely colored faceted gems sit at the top of the range, while everyday cluster and tumbled material remains one of the best values in the crystal world.

Two kinds of imitation come up most often. The first is synthetic amethyst — quartz grown in a laboratory by a hydrothermal process. It is chemically identical to natural amethyst and genuinely is quartz, so simple hardness and fracture tests will not distinguish it; lab-grown material is often unusually clean and evenly colored, and reliably separating it from natural amethyst can require gemological testing. The second is dyed glass sold as amethyst, which is far easier to catch.

Glass gives itself away. Look for tiny round bubbles trapped inside (quartz crystals do not contain spherical bubbles), a too-perfect, uniform color with no natural zoning, and rounded or molded edges rather than true crystal faces. Glass also tends to feel slightly warmer to the touch than quartz, which feels cool, and it is softer, so it can be scratched by a quartz point or a steel file. With dyed quartz, the dye often concentrates in cracks and fractures, showing as thin lines of more intense color — a clear sign the purple was added rather than grown.

Amethyst is hard (7) and physically durable, so it resists scratches and is easy to live with, but it has one real weakness: light. Prolonged, strong sunlight can gradually fade amethyst's purple toward gray or colorless, so it is best kept out of permanently sunny windows and displayed in indirect light. Heat is the other thing to avoid — strong heat will change the color, turning amethyst yellow, orange or brown; in fact much of the "citrine" on the market is heat-treated amethyst.

For everyday cleaning, warm water and a soft cloth or brush with a little mild soap are all that is needed. Avoid harsh chemicals and sudden temperature changes, and do not assume an amethyst is safe in an ultrasonic cleaner. Stored away from direct sun and treated gently, an amethyst will keep its color and polish indefinitely.