With close microscopic examination of inclusions and defects, yes you probably can. There are also spectroscopic differences. In general looking at finished jewelry, no, not really.
> With close microscopic examination of inclusions and defects, yes you probably can.
With good laboratory instrumentation, you might be able to distinguish between them -- i.e. note that they're not perfectly identical, that they are distinguishable -- but, unless you are an expert, you would be unable to tell which of the two is the natural stone.
Yes, you need to know which features are evidence of mined vs. synthetic/lab grown. Although there is equipment now preloaded with software that can discriminate. I think its based on photoluminescence.
De Beers sells devices that can distinguish between naturals and CVD synthetics. They're not cheap, but less than ~$80K, IIRC. They do a pretty good job, I've heard >90% success in identifying CVD stones.