Diamonds & Diamond Grading Chart GIA

 


 

National Gemstone markets diamonds with GIA Grading Reports. The GIA was formed in 1931 and is a non-profit institution. They do not buy/sell or appraise diamonds. They are an educational and research institute. Please note, a diamond graded by a person who graduated from the GIA is not the same as a GIA Grading Report. Do not buy a diamond from anyone who grades and sells it. There is too much temptation to over-grade the diamond. The GIA operates like a neutral intermediary between the buyers and sellers.


The GIA created the first, and now globally accepted standard for describing diamonds, the 4 "C"s. Today, the 4 "C"s of Diamond Quality is the universal method for assessing the quality of any diamond, anywhere in the world.

 

The Four "C"s

Color

Cut

Clarity

Carat Weight

Shape and Cut
Each diamond is described as to its shape (round, oval, pear, etc.) and its cut (brilliant, etc.)

Weight
Diamonds are weighed on an extremely accurate digital balance. One carat equals 100 points, which weigh 1/5 gram.

Proportions
The items in this category relate to the cut (or make) of the diamond:

  • Depth Percentage: The relationship between the depth and the average diameter of a diamond.
  • Table: The relationship between the table (flat, top facet) and the average diameter.
  • Girdle: Describes the variance and relative width at minimum and maximum positions. The girdle is the rim that separates the top and the bottom of the diamond.
  • Culet: The bottom facet of a diamond as viewed through the table.
  • Polish: Refers to the quality of the surface of a diamond.
  • Symmetry: General comment regarding the symmetry of the diamond.

Clarity
GIA Clarity Grading Scale

IF

VVS1...VVS2

VS1...VS2

SI1...SI2

I1...I2...I3

INTERNALLY FLAWLESS

VERY,VERY SLIGHTLY INCLUDED 1 AND 2

VERY SLIGHTLY INCLUDED 1 AND 2

SLIGHTLY INCLUDED 1 AND 2

INCLUDED 1, 2 AND 3

**Clarity refers to the summation of the number, size and placement as well as the nature of inclusions and/or surface irregularities. Flawless stones are diamonds free of inclusions under 10X power. Internally flawless are diamonds without any internal inclusions. VVS1 and VVS2 have extremely small inclusions. VS1 and VS2 possess small inclusions. SI1 and SI2 have inclusions that can be seen easily under 10X power magnification, but are not usually visible to the naked eye. I1, I2, and I3 have large inclusions that are visible to the naked eye.

Color Grade
GIA Color Grading Scale

D..E..F

G..H..I..J

K..L..M

N..O..P..Q..R

S..T..U..V..W..X..Y..Z

COLORLESS

NEAR COLORLESS

FAINT YELLOW

VERY LIGHT YELLOW

LIGHT YELLOW

**Color refers to the absence of color in a diamond. The less yellow within the diamond, the higher on the alphabetical scale the diamond will be graded. Colorless diamonds are D-F, near colorless are G-J, faint yellow are K-M, very light yellow are N-R. S-Z are light yellow.

Fluorescence
Fluorescence describes the degree of sensitivity of a diamond to long wave ultraviolet radiation. Diamonds have been known to fluoresce in a variety of colors, such as pale blue, green, yellow, and rarely red.

**Please be aware of the following: Some Diamonds may have what is called a "natural." There is nothing "natural" about it. A small portion of the original Diamond crystal surface is left unpolished on the girdle of the gemstone. This area, which is called a "natural," indicates that little material was wasted in cutting to obtain a heavier carat weight. Its presence is not desirable on a polished Diamond.

 

What Are TTLB & TTLC Diamonds?

 

TTLB: Top Top Light Brown

TTLC: Top Top Light Cape

 

TTLB diamonds have a very slight brown tint to them. They do not have a yellow tint. TTLC diamonds have a definite yellow tint to them. Cape diamonds get their name from the area of Africa where they were typically found. Both of these colors of diamonds will be less expensive than commercial white diamonds of equivalent size, weight, shape, and clarity. They can very often offer the consumer great value for their money. They are best set in yellow gold mountings, as the color contrast will be more apparent when they are set in white gold mountings. These colored diamonds are not in the category of "Fancy Colored Diamonds."

 

Fancy Colored Diamonds


How Do Naturally Colored Diamonds Get Their Colors?

 

Diamonds  with 100% natural color can be found in all colors of the rainbow. Their colors are caused by trace impurities of other minerals, exposure to radioactive minerals, or by irregular growth patterns within the crystal. Some of the most popular natural colors are shades and combinations of pink, blue, brown, yellow, orange, green, red, and all kinds of hues in-between. A few examples of how they get their colors are listed below.

***A variety of colors can be produced by irradiation or by artificial bombardment of electrons or neutrons. Electron bombardment produces a blue color, while neutron bombardment produces a green color. In turn, the enhanced blue and green colors can then be heat treated, which changes their color to yellow or brown. With the popularity and demand for colored Diamonds, many artificially colored Diamonds are being sold as “natural.” As with any Diamond you are buying, make sure you know what you are buying! The naturally colored Diamonds are very expensive, so if the price seems too cheap, it’s probably artificially colored. Caveat Emptor!

 

Fancy Yellow Diamonds (Canary Yellow and Other Similar Hues)

 

Fancy Yellow Diamonds owe their color to the presence of Nitrogen and/or Hydrogen impurities, which absorb the blue end of the color spectrum. Inclusions of Iron may also yield a yellow colored Diamond.

 

Brown/Cognac Diamonds (Champagne, Chocolate Hues)

 

These Diamonds also owe their color to Nitrogen and/or Hydrogen impurities. Inclusions of Iron may also yield brown colored Diamonds. They come in many different shades of brown.

 

Pink Diamonds (Pink, Lilac, Purple Hues)

 

The pink color within these rare Diamonds is due to irregular crystal growth patterns, which cause microscopic imperfections within the lattice structure. Inclusions of Manganese may also yield pink and red colored Diamonds.

 

Green Diamonds (Green, Yellowish-Green, Grayish-Green Hues)

 

Green Diamonds owe their hue to millions of years of exposure to naturally occurring gamma and/or neutron radiation, and are typically found in alluvial secondary deposits. Most Green Diamonds are actually a yellowish-green, grayish-green, or a combination of the two. They may also have come into contact with radioactive minerals, such as Uranium, through natural irradiation of the earth.

 

Blue Diamonds (Sky Blue, Rich Deep Blue Hues)

 

These beautiful shades of blue owe their colors to trace impurities of Boron. The blues are the most frequently irradiated colors found on the market. Be aware of what you are buying!

 

Chameleon Diamonds (Pleochroic ~ Color Change Diamonds)

 

These are very rare olive-grayish color changing, or pleochroic Diamonds. Because of their color changing properties they are referred to as “Chameleon Diamonds.”  Their color changes hue from grayish-blue or olive-green to yellowish-green or straw-yellow under different lighting conditions, lighting color temperatures, and/or ambient temperature changes. Chameleon Diamonds can be made to temporarily change color to a yellowish-green by exposing them to heat (150º C to 250º C), or by short-term storage (up to 24 hours) in total darkness. Exposure to direct sunlight will bring out the olive-green color. The color change effect is temporary, and will totally reverse itself when the conditions re-stabilize. You can do this process over and over again with the same results, just as you can with Alexandrite. It is believed that the color changing effect is due to a higher than normal amount of hydrogen impurities.

 

Round Diamond Sizes and Variable Weights**

 

**Not all diamonds are cut correctly, so there may be differences between the standard, or ideal sizes and carat weights. This occurs when a diamond is cut too deeply or too shallow. Improper cutting may also interfere with the brilliance of the stone, as the light cannot reflect back properly. Below are two tables showing the differences between the millimeter sizes and the carat weights of diamonds on average. There is also an illustration below showing the differences in how the light can or cannot reflect back properly in a stone cut improperly.

 

Diamonds Weighing .01-.50 Carats

 

Carat Size

Normal Range (ct)

Normal Range (mm)

.01

.0071-.012

1.2-1.4

.015

.013-.017

1.5

.02

.0175-.023

1.61-1.75

.03

.026-.035

1.9-1.95

.04

.036-.045

2.0-2.2

.05

.046-.065

2.25-2.4

.07

.066-.085

2.55-2.7

.10

.086-.115

2.85-3.0

.12

.116-.135

3.1-3.2

.15

.14-.17

3.25-3.5

.20

.18-.22

3.6-4.0

.25

.23-.27

3.9-4.3

.33

.30-.35

4.2-4.6

.40

.38-.43

4.5-4.9

.50

.48-.55

4.9-5.3

 

 

Diamonds Weighing .60-1.50 Carats

 

Carat Size

Approximate Millimeter Size

.60-.65

5.5-5.6

.75

5.8-6.0

.85

6.0-6.4

1.00

6.3-6.5

1.25

6.8-7.0

1.50

7.2-7.5

 

 

Diamonds Weighing 2.0-7.0 Carats

 

Carat Size

Approximate Millimeter Size

2.0

8.0-8.2

3.0

9.35-10.0

4.0

10.3-10.8

5.0

11.0-11.5

6.0

11.75-12.0

7.0

12.4-12.6

 

*Table 3 Courtesy of “Gems and Jewelry” by Joel E Arem and "Tripps Manufacturing"
**Of course there are many other variations in sizes and weights in-between those listed above.

 

Famous Large Diamonds

 

Carats

 

Color

Name

Origin

530.20

White

Cullinan I

South Africa

407.48

Yellow

Un-Named

Africa

317.40

White

Cullinan II

South Africa

280.00

White

Great Mogul

India

277.00

White

Nizam

India

250.00

Pink

Great Table

India

245.35

White

Jubilee

South Africa

234.50

Yellow

Debeers

South Africa

228.50

Yellow

Victoria 1880

South Africa

205.00

Yellow

Red Cross

South Africa

202.00

Black

Black Star Africa

South Africa

189.60

White

Orloff

India

185.00

Pink

Darya-I-Nur (Iran)

India

184.50

White

Victoria 1884

South Africa

150.00

White

Light of Peace

Sierra Leone

150.00

White

Darya-I-Nur (Dacca)

India

140.50

White

Regent

India

137.27

Yellow

Florentine

India

128.51

Yellow

Tiffany

South Africa

127.02

White

Portugese

Brazil

125.65

White

Jonker

South Africa

108.83

White

Koh-I-Noor

India

94.40

White

Cullinan III

South Africa

71.73

White

Lesotho

Lesotho

70.20

White

Idol’s Eye

India

69.42

White

Taylor-Burton

South Africa

67.89

Champagne

Transvaal

South Africa

60.00

Pink

Nur-Al-Ain

India

55.00

White

Sancy

India

45.52

Blue

Hope

India

41.00

Green

Dresden

India

35.32

Blue

Wittelsbach

India

31.00

Blue

Eugenie Blue

India

23.60

Pink

Williamson

Tanzania

12.42

White

Uncle Sam

Arkansas

 

Courtesy of “Gems and Jewelry” by Joel Arem

 

**Chemically Diamonds are pure Carbon, the same as Graphite, a soft mineral used in pencils. The dramatically different properties of the two minerals are caused by the chemical bonding of Carbon atoms. The atoms are bonded strongly in Diamonds, and weakly in Graphite. Diamonds are extremely stable under ordinary conditions, but unlike other crystalline gemstones, when they are heated to red hot in air they will literally vanish to form carbon dioxide.

 

The Anatomy of a Gemstone


**The above illustrations show the Round Brilliant Cut faceted gemstone. It is the most modern, ideal, and popular cut for Diamonds. It was developed in 1910 and has the following characteristics: a round girdle, at least 32 facets on the crown and table, at least 24 facets, and sometimes a culet (a very small facet at the point) on the pavilion. It may also be referred to as the Tolkowsky Brilliant Cut. This round cut must have 57-58 total facets to be called a Round Brilliant Cut. Other popular Diamond and gemstone cuts are shown on my Gemstone Grading GIA web page.

 

 

Properly and Improperly Faceted Diamonds Illustration**


 

**As seen in the above illustration, a gem properly proportioned with respect to its refractive index will reflect back the light that enters it, yielding maximum brilliance. Light leaks out of a gem cut too shallow or too deep, diminishing its brilliance. Please see my "Gemstone Clarity Grades GIA, Mohs Hardness Scale & Much More" page for an illustration of gemstone cuts and how the light passing through a clear gemstone reacts when it is cut properly.

 



 

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