Synthetic gemstones have same chemical and optical properties as natural gemstones. The only difference among them is inclusions.
From the astrological point of view, a gemstone is said to endow powers when light (natural sunlight) enters from gemstone through to the body.
Since both natural and synthetic gemstones have same chemical bonding and when light enters in gemstone it passes through the same chemical bonding structure before entering in the body, i.e. why it is obvious that synthetic gemstone has same astrological powers as natural gemstones.