The easiest way: only buy crystals from merchants you trust. Reputable mineral dealers do not even offer synthetic or colored goods. But even without expert knowledge, you can find out whether it could possibly be a sham.
TRUST YOUR INTUITION
Crystals have a unique aura that you can usually feel. Take the stone in your hand and focus on its energy - if you don't feel anything or the weight in your hand doesn't feel right, it may be glass or synthetic.
BEWARE OF UNNATURAL COLORS
Natural crystals come in all colors of the rainbow - and sometimes, with a bit of luck, you may even catch a specimen with a small prism shimmering inside. However: If the stone is bright pink throughout or even the outside of the geode is colored throughout, chemistry was probably involved. Unfortunately, the dazzling Aqua Aura crystal is also an unnatural phenomenon. They are vaporized crystals and druses, often of poor quality.
THE USUAL SUSPECTS
You should take a closer look at these stones, because people often cheat with them. Citrines are often just burnt amethysts. You can tell this because they have the typical drusen shape of amethysts and are a dull yellow-orange. Opals are very valuable and expensive, cheap versions are usually synthetic opal glass. Agates usually have a rather unsaturated color spectrum from brown to blue, bright models are almost always colored. Inexpensive turquoise is almost always a synthetic product made from powder - a bite into the stone reveals whether it is a soft and pliable fake.
Since you can't hold the crystal in your hands to experience its vibration and aura in person, choosing a stone online can be a real challenge. We recommend that you intuitively choose the stone that inspires at first sight. Color plays an important role here - the effect of the crystal is strongly dependent on its coloring. Conversely, this means: If you like the color of a stone or a set of stones, you will most likely also like the aura of the stone.