There are plenty of stones in the world, but at this moment only four are classified as precious stones. These are: sapphire, ruby, emerald and diamond, which all score above 7 on the Mohs scale. The most obvious way to distinguish an authentic stone from an imitation is to have it appraised by a gemmological laboratory, but not everyone wants to waste their time. There are simpler ways, but they will not be as accurate as the mentioned expertise.
There are three quick and easy ways to check the authenticity of a gemstone versus its imitation.
The first is to examine it under a magnifying glass to find various inclusions and imperfections. If they are present, the stone is genuine because it was underground and someone had to dig it out. The synthetic ones will be perfectly smooth.
The second way is to check the resistance to scratches. Just run a coin over it and if there are no more scratches on the stone, it is a real gemstone.
The last way is to check its colour and light reflection. A real ruby has a vivid bright red color, its imitations are cloudy and dull. Sapphire has a deep blue color and reflects no other color besides it, its fakes are brighter and with more luster. Emerald has a green-blue hue with deep carbonation or green-yellow with moderate carbonation.
In addition, there are bubbles, which are only found in imitations. In the case of a diamond it is worth checking how it refracts light. It is enough to put it on a piece of paper with some text, if we can see the letters or they are slightly blurred it is a fake. A real diamond refracts the light in such a way that it would be impossible to read any text.