Unfortunately in today's world, fraud happens. Glass and synthetic gems are sold as real stones or natural stones. If you aren't a lapidarist then you might not know how to tell whether the stone you have is real or fake. As a general rule of thumb, real gemstones no matter what kind they are have inclusions. You may not be able to see the inclusions without a loupe or magnifier since higher graded gemstones have fewer inclusions.
What are inclusions?
Inclusions are any material that's been trapped inside a mineral. We often consider this clarity. In natural gemstones, needles, clouds, fluids, and crystals are most common to appear. Some gemstone types are easy to test for inclusions like jade. If you hold jade up to a light you'll notice what looks like fibers or needles running throughout.
If you can't see any inclusions with the naked eye that's okay. Another way to test your gemstone or pearl is by temperature. Leave the stone you'd like to test sitting out, untouched for a while. When you pick it up you should notice the stone feels cool but it will quickly warm up to match your body temperature. Fake stones of course won't change temperatures.
The best way to be sure is by purchasing from reputable retailers. If you think that the price is too good to be true, it probably is.