below pix: a boule of synthetic ruby created by flame fusion method (at top) with cut samples (at bottom)

Synthetic (or "created"
) gemstones are grown in a laboratory instead of being formed in the ground by nature. They are physically and chemically identical to natural-grown gems but cost much less to produce and to buy.
Just like natural gems, synthetics vary tremendously in quality. Using low-quality processes, synthetic sapphires and rubies can be created for
less than a dollar a carat, whereas high-quality (or "luxury"
) synthetics can cost a hundred times more to create and sell for several hundred dollars a carat at retail.
METHODS TO CREATE SYNTHETIC GEMSTONES:
Flame Fusion Method 
The first technology utilized for growing gemstones in a laboratory, flame fusion is still very widely used to create rubies, sapphires, and spinel. It's inexpensive, but yields low quality gems. These created gems are often used in "class rings" and cheap jewelry found in discount stores. It's relatively easy for any competent jeweler to detect synthetics created by flame fusion methods because the "dripped" molten material forms "growth striae" (thin, narrow grooves) as it hardens
Pulled-Growth 
Czochralski pulled-growth is also commonly used to create rubies, sapphires, and spinel. It's a more complex and costly method, and creates better gems than flame fusion.
Still, both these methods yield gems of questionable quality. Because they use very high temperatures, it is difficult for manufacturers to achieve uniform color (particularly in rubies and blue sapphires). The mechanical action of melting and reforming crystals introduces non-uniformities in the gems, which scatter light and give the stone a "dead" look - like a piece of colored glass.
Flux Method 
In addition to creating the "big three" (emerald, ruby, and sapphire), the flux method is used to grow spinel and alexandrite. This method uses a supersaturated chemical bath to form the crystals. Flux Method or Flux Fusion - not to be confused with Flame Fusion - creates the highest quality and most expensive synthetic corundum (rubies and sapphires).
Hydrothermal Method 
High quality emerald, as well as the less common aquamarine, morganite, and beryl, can be lab grown by the hydrothermal method. It uses a water solution at very high temperature and pressure and takes several months to create a batch of gems. That's one of the reasons higher quality created gems cost so much more.