GIA,
In their own words,
 “The Worlds Foremost Authority in Gemology” as their registered trademark.

You will find references to GIA or Gemological Institute of America.
We supply with all of our pieces, a certificate of authenticity and retail value. This certificate is prepared by a GIA trained appraiser.

The GIA is the leading authority on Gems. Established in 1931, is the worlds leading authority on gems. The GIA is a non-profit institution, created to “ensure the public’s trust in gems and jewelry”. The GIA does this through, “by upholding the highest standards of integrity, academics, science, and professionalism through education, research, laboratory services, and instrument development.”

Some of the more famous gems identified and graded by the GIA:

Some of the more celebrated stones graded by GIA include: the Hope Diamond (45.52 carats), the Steinmetz Pink (59.60 carats), the Taylor-Burton Diamond (69.42 carats), the Allnatt (101.29 carats), the De Beers Millennium Star (203.04 carats), the Centenary Diamond (273.85  carats), and the Incomparable Diamond (407.48 carats).