As previously mentioned, even a reputable jeweller cannot tell the difference between a lab grown diamond and an earth-extracted diamond using a standard 10x loupe and regular lighting.

Most jewellers have instruments to separate diamonds from cubic zirconia and moissanite. Until now, these have done a good job, but they cannot separated lab grown and earth mined diamonds.

There are a few higher end instruments such as one De Beers produce that use shortwave ultraviolet light and cross polar filters to determine the difference in crystal growth structure of a lab grown diamond verses a mined diamond. De Beers Diamond View tool costs over $50,000 and is mostly used by independent laboratories such as the Gemological Institute of America (GIA) and the International Gemological Institute (IGI). Recently lower priced testers (or separators) have appeared on the market which can distinguish between lab grown and earth mined diamonds and since the differences are extremely difficult to detect, unless a skilled and experienced operator carries out the separation,  it could result in an incorrect decision.

As mentioned, there are readily available instruments on the market used to separate cubic zirconia and moissanite from diamond. There are two main types of testers that jewellers typically use. The first type of instrument checks for thermal conductivity and is intended to separate CZ and diamond. All lab grown diamonds will be correctly identified as diamonds by these thermal testers. (As will earth mined diamonds).

The second type of tester checks for electrical conductivity. Moissanite is electrically conductive, while mined diamonds are not, so this tool usually separates the two. But this can be misleading because all blue diamonds are electrically conductive, due to the presence of boron in the atomic structure and will incorrectly identify as moissanite on these testers. The reason that mined diamonds are not electrically conductive is that over 98% of mined diamonds have significant nitrogen impurities in the diamond crystal.