<P> Each laboratory has its own methodology to evaluate gemstones . A stone can be called "pink" by one lab while another lab calls it "padparadscha". One lab can conclude a stone is untreated, while another lab might conclude that it is heat - treated . To minimise such differences, seven of the most respected labs, AGTA - GTL (New York), CISGEM (Milano), GAAJ - ZENHOKYO (Tokyo), GIA (Carlsbad), GIT (Bangkok), Gübelin (Lucerne) and SSEF (Basel), have established the Laboratory Manual Harmonisation Committee (LMHC), for the standardization of wording reports, promotion of certain analytical methods and interpretation of results . Country of origin has sometimes been difficult to determine, due to the constant discovery of new source locations . Determining a "country of origin" is thus much more difficult than determining other aspects of a gem (such as cut, clarity, etc .). </P> <P> Gem dealers are aware of the differences between gem laboratories and will make use of the discrepancies to obtain the best possible certificate . </P> <P> A few gemstones are used as gems in the crystal or other form in which they are found . Most however, are cut and polished for usage as jewelry . The picture to the left is of a rural, commercial cutting operation in Thailand . This small factory cuts thousands of carats of sapphire annually . The two main classifications are stones cut as smooth, dome shaped stones called cabochons, and stones which are cut with a faceting machine by polishing small flat windows called facets at regular intervals at exact angles . </P> <P> Stones which are opaque or semi-opaque such as opal, turquoise, variscite, etc. are commonly cut as cabochons . These gems are designed to show the stone's color or surface properties as in opal and star sapphires . Grinding wheels and polishing agents are used to grind, shape and polish the smooth dome shape of the stones . </P>

Parts of the surface of a gem stone