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Diamonds - GIA Classification
CLASS
I American/Tolkowsky Cut
Table: 53-60%
of diameter of stone for round, marquise, pear and oval; 58-64%
of diameter of stone for emerald and rectangular
Total depth: 59.3-61%
of diameter of stone for round, marquise, pear and oval; 58-64%
of diameter of stone for emerald and rectangular
Crown angle: 34-35
degrees for round, marquise, pear and oval 33-35 degrees for emerald
and rectangular
Crown height: 13.5-16.2% of diameter of stone
for round, marquise, pear and oval and 11.7-16.2%
of diameter of stone for emerald and rectangular
Girdle thickness:
.7-1.7% of diameter of stone (medium)
Pavilion angle:
40.20 to 41.20 degrees for rounds; 39.25 to 40.75 degrees for marquise,
pear and oval; 43.8 to 46.8 degrees for emerald and rectangular
Pavilion depth:
42.52-43.57% of diameter of stone for round, marquise, pear and
oval; 47.6-53.1% of diameter of stone for emerald and rectangular
CLASS
II
Table: 53-64%
for round, pear, marquise and oval; 53-65% for emerald and rectangular
Total depth: 56-61%
for round, marquise, pear and oval; 56-65% for emerald and rectangular
Crown angles: 32-35
degrees for all shapes
Crown height: 11.2-16.2%
for all shapes
Girdle thickness:
Thin to thick for all shapes (medium preferred)
Pavilion angle:
40 to 41.5 degrees for rounds; 39.25 to 40.75 degrees for pear,
marquise and oval; 43.3 to 46.8 for emerald and rectangular
Pavillion depth:
42.31-43.89% for rounds; 41.51-43.1% for pear, marquise and oval;
47.1-53.1% for emerald and rectangular
Polish & symmetry:
Good
CLASS
III
Table %: 65-70%
for round, marquise, pear and oval; 66-70% for emerald and rectangular
Crown angles: 30-32
degrees for all shapes
Girdle thickness:
Very thin or very thick for all shapes
Pavilion angle:
Any measurement other than 40 to 41.5 degrees for rounds or 39.25
to 40.75 degrees for marquise, pear and oval; any measurement other
than 43.3 to 46.8 degrees
Polish & symmetry:
Fair to good
CLASS
IV (50-60% below cost)
Table %: 70% and
above for all shapes
Crown angles: 30
degrees and below for all shapes
Girdle thickness:
Extremely thin to very thin or very thick to extremely thick for
all shapes
Pavilion angle:
Any measurement other than 40 to 41.5 degrees for rounds or 39.25
to 40.75 degrees for marquise, pear and oval; any measurement other
than 43.3 to 46.8 degrees
Polish & symmetry:
Fair to poor
by Fred Cuellar,
author of the best-selling book "How to Buy a Diamond." More questions?
Ask the Diamond Guy®
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