As per gemology, synthetic gemstone has the same composition, chemical, physical & optical properties like lustre, refractive index, specific gravity etc. The only difference is inclusions.
As per astrologers; synthetic gemstones made in lab do not have same astrological powers maybe because it didn’t take thousands of years to develop naturally but took only few days or hours to get it made in lab.
Even being a gemologist and knowing all those things, I personally would like to wear natural gemstones instead of synthetic gemstones for astrological purpose.