The microscope remains the most important tool in gem identification. A thorough and detailed analysis reveals a lot of information about a gem - it has a story to tell - about its origin - the depth within the earth's crust, the temperature and pressure conditions, the chemical environment in which it has formed, and much more. Observation of internal features is still the most valuable technique in identifying the nature of a gem. In some cases, the features are so characteristic, that they not only tell the identity of a gem, but also its origin. Microscopy remains the core of any gemmological study and complements 'the many' spectroscopic analytical tools, in determining the nature, whether natural or synthetic and the type and degree of treatments performed. At the Gem Testing Laboratory, every analysis is started with a detailed microscopic observation.
It is mainly the inclusion study which reveals most of the information about a gem. The inclusions are the physical impurities present in a gem and are of utmost importance to a gemmologist, while the most undesirable object for a gemstone cutter or even a jeweller. The inclusions for simpler understanding, can be divided on the basis of phases of matter such as solid, liquid or gaseous and their combination (referred to as 'phase' inclusions) and structural (such as growth or colour zoning, twinning planes, etc). For a detailed study and understanding of inclusions, every gem enthusiast will always refer to the three volumes of 'Photoatlas of inclusions in gemstones' by Gübelin & Koivula.
Here, are some of the common examples showing the importance of microscopy.
Identification of gemstone species
Spot the difference! Rutile silk in ruby (left) and in almandine garnet (right) looks identical, but careful observation of angle of intersections can reveal the difference. The needles in ruby or corundum intersects at 60/120o, while 70/110o in an almandine garnet.
Separating natural from synthetic counterparts
Identifying treated gems
Fracture filling in emeralds
Clean fracture in emerald showing iridescence (top, left), oiled fracture (top, centre & right) showing dendritic patches and uneven filling and resin-filled fractures showing blue and golden flashes (bottom). Conclusion is however, drawn in conjunction with FTIR analysis
Heating in rubies and sapphires
A zircon crystal in a natural unheated sapphire with a radiation-induced stress crack (left) appear transparent, but on heating at elevated temperatures, zircon crystal gets damaged and appear white and frosty, often forming a highly reflecting discoid fracture (centre) and / or atoll-like halo (right).
Microscopy is basically the core of whole gemmological analysis of a gemstone, as it assists other techniques in validating the data.