Use a 10x loupe to see whether the lab grown diamond is mono-refractive or birefringent. lab grown diamonds are mono-refractive stones, while moissanites are birefringent. If you look down from the table to the pavilion of the lab grown diamond with a 10x loupe, you can see that the prongs near the bottom tip are overlapping, or if you can see that the prongs near the bottom tip are overlapping from the kite surface at an angle, then it is probably moissanite, not lab grown diamond.
*One carat is equal to 0.2grams.
*The waist diameter of the diamond will be affected by the cutting method and proportion. So the same weight diamonds may have different waistlines.
Specific gravity liquid: The specific gravity of lab grown diamond and moissanite are not the same, so you can distinguish them by using specific gravity liquid, but only for unset stones. (The chemical composition of the specific gravity liquid is diiodomethane, which is highly toxic, so you should be especially careful in using it.)