Laser Induced Breakdown Spectroscopy (LIBS) for gemological testing: the case of corundum gems

In gem testing routine, one of the main requirements is to obtain the maximum amount of information without sample preparation. Even the classical gemological methods allow usually identifying the mineralogical identity of a gem, the possibility to inspect aspects as provenance of natural gemstone, and invasive and blind treatments often require the application of more sophisticated methods able to give back quantitative information [1]. Moreover, due to the development of more and more refined synthesis method, the discrimination between natural and synthetic gems is not trivial. Among gemstone analysis techniques, Laser Induced Breakdown Spectroscopy (LIBS) is increasingly worth considering; the method, already tested for example in origin determination of emeralds [2] or detection of Be-diffusion treatment in corundum [3], provides rapid results on trace-element contents, the latter considered a fingerprint of a gem. Moreover, determining a minimal damaging (an ablation area of just few micrometers), it can be extensively used on both cut and raw gemstones. In this prospective, the present paper intends to contribute the researches in gems analytics providing the results of LIBS measurements on a meaningful sampling of natural (both cut and raw specimens) and synthetic rubies and sapphires, highlighting the potential of the method in helping gemological laboratories for the fast, easy, micro-destructive and reliable discrimination between natural and synthetic corundum, as well as provenance determination.