There is nothing quite like the thrill of turning a new crystal over in your hands, holding it up to the window and watching the light catch inside it. But that thrill can curdle quickly if you later realise the stone you paid good money for is dyed glass, resin or a heat-treated pretender. The good news is that most common imitations give themselves away with a little patience and a few simple checks you can do at home or at the shop counter.

Start with Weight, Temperature and Feel

Before you look at anything else, let your hands do the first test. Pick up the stone and compare it with a genuine piece you already own of a similar size. Quartz and most silicate minerals are comparatively dense, so a real tumble of amethyst feels satisfyingly solid — heavier than your eye expected. Resin copies feel almost hollow by comparison, and glass tends to feel a touch lighter than true quartz, with a slightly slippery, soapy smoothness rather than a cool, mineral hardness.

Temperature matters too. A genuine stone sitting on a shelf takes a few seconds to warm to your skin, and the coolness lingers at its centre. Resin is at room temperature almost instantly. Try holding a piece for a slow count of ten: if the coolness has vanished within two or three seconds, be suspicious. This test works best on larger pieces — small chips and points are too tiny to tell reliably.

Dyed Glass, Resin and Reconstituted Stone

Glass and resin account for the overwhelming majority of fakes sold online and at markets, and each leaves its own fingerprints.

• Bubbles: Glass often contains perfectly round, evenly spaced bubbles suspended inside. Natural inclusions are irregular — angular, cloudy, or shaped like tiny needles and leaves.
• Mould seams: Run a fingernail around the edge of the stone. Resin figures are cast in moulds, so you may feel a thin raised line where two halves met, or a flat, unnaturally smooth base.
• Scratch test: A fingernail will mark resin and most soft imitations, but it will not touch quartz, jasper or agate. Try it somewhere discreet.
• Colour pooling: Dyed glass and dyed quartz tend to hold their brightest colour in cracks, chips and drill holes. Look at the edges under a bright lamp — if the dye is concentrated in the fault lines while the rest of the stone is pale, that is a clear giveaway.
• Reconstituted stone: This is crushed rock bonded with resin. It looks grainy, dense and oddly uniform, with colours that bleed into one another rather than sitting in crisp bands.

Heat Treatments, Dyes and Coatings

Not everything altered is a fake, but the alteration should be disclosed and the price should reflect it. Heat-treated amethyst sold as citrine is the classic example: genuine citrine is a pale lemon to smoky gold, while the baked version is a deep burnt orange with colour concentrated in the tips and a slightly metallic sheen. If the point is inky orange at the end and nearly colourless at the base, you are almost certainly looking at heated amethyst.

Dyed agate slices are another familiar offender. The bands are unnaturally vivid — hot magenta, neon turquoise — and the dye does not follow the natural growth rings. It sits in the porous layers and along the fractures instead. Coated stones such as "aqua aura" quartz are simply quartz with a thin metallic film bonded to the surface; the coating will not survive a gentle rub with a fine file at the base of the point, whereas the stone underneath will.

Check Inclusions, Growth Lines and Surface Texture

Real minerals record their history inside. Quartz commonly shows veils, phantoms, tiny mineral flecks, and hairline fractures that flash rainbow colours under a light. Perfectly clear, large and flawless stones at bargain prices should make you pause — that combination is genuinely rare and expensive.

Look at the surface as well. On a quartz point, run your fingertip down one of the long sides: genuine crystals usually have fine horizontal growth striations you can feel as ridges. Fakes are usually glassy-smooth or covered in mould texture. Finally, remember that nature does not make identical twins. If a tray of points all share exactly the same shade, shape and size, they came from a factory, not a mine.

Price, Provenance and Reference Guides

Price is not proof of authenticity, but a price that seems too good is usually exactly that. Compare the cost per gram or per kilogram against several sellers for the same material. Rare minerals such as malachite, lapis with pyrite, and high-grade rose quartz should never be sold by the basketful at pocket-money prices.

Spend an afternoon with a trusted reference guide — a well-regarded crystal directory, a mineralogy field guide, or the collections at a local museum or lapidary club. Learn the look of five or six stones you love and handle genuine examples wherever you can. Ask sellers directly whether a stone is dyed, heated or coated, and buy from those who answer plainly.

A Practical Buying Checklist

• Weigh it against a known genuine stone of similar size.
• Hold it and time how long the coolness lasts.
• Look for round bubbles, mould seams and unnaturally smooth bases.
• Inspect the edges and cracks for pooled dye.
• Check growth striations on quartz points with your fingertip.
• Compare the price per gram with at least three other sellers.
• Ask about treatments — heat, dye, coating, reconstitution — and expect a straight answer.

With a little practice these checks become second nature, and your collection will be all the more rewarding for it.