According to the FTC, any gemstone whether created in nature or in a lab can be classified as “real” if it contains identical mineral makeup. This means that synthetic gemstones are classified and sold as “real”, although not as “natural”. To be labeled natural, stone must be produced by nature.
Natural Gemstones:
The term Natural refers to a gemstone that is found growing/produced in
the natural world without the influence of human activity. These would
be gemstones mined from the earth as well as those discovered naturally
occurring in the water (such as pearls and coral). Natural gems have the
allure of rarity when compared to their synthetic counterparts – a
natural pearl harvested from the ocean can be hundreds if not thousands
of times more expensive than its synthetic counterpart. A natural star
sapphire, likewise, will be at a premium because of its rarity next to a
lab created star sapphire.
Synthetic / Lab Created or Grown Gemstones
Synthetic gemstones, sometimes called cultivated, cultured, man-made,
lab-made, or lab-created gemstones, get their name because they are
produced in laboratories. These labs use advanced techniques to recreate
in a controlled setting the time, pressure, and temperature on carbon
and different elements to produce different types of gemstones. What is
the most interesting about synthetic stones is that scientifically, they
are chemically identical in properties to the gemstones that are found
in the Earth.
Simulants and Imitations
If a lab-created gemstones contains other materials, however, such as spinel being passed off as a ruby, the gemstone is not considered real and is usually called ‘simulated’ rather than “synthetic” by the seller. Simulated gemstones may also include natural gems passed off as others.
Source:https://www.jewelerstoolsmall.com/article-110-How-to-Tell-Natural-Synthetic-Gemstones.html