Diamond Glossary

The knowledge and more information you have the better diamond purchase you will make. Here are a number of diamond terms that are used by jewelers to describe diamonds and which appear on diamond grading reports.

I:

Inclusion:
A clarity characteristic found within a diamond. Most inclusions were created when the gem first formed in the earth. An impurity within a diamond, such as a spot or irregularity in the crystal structure of the stone. These can include a cloud, a fracture, another diamond inside the bigger one, liquid, etc. Inclusions can either be visible with the naked eye (usually SI-3 clarity and below) or visible only under magnification. Fewer inclusions means a finer clarity grade, increased rarity, and increased value.

Included Crystal:
A mineral crystal contained in a diamond.

Internal Graining:
Internal indications of irregular crystal growth. May appear milky, like faint lines or streaks, or may be colored or reflective.

Irradiated diamond:
A diamond which has been exposed to radiation.

Imitation:
Any diamond like material, either natural or artificial, which is marketed as look-alike for a natural diamond. i.e. Glass, - zirconium, YAG, GGG, moissanite etc.

Ideal Cut or American Cut :
"Ideal" also known as the "American Ideal Cut", a cutting style that is based on the Tolkowsky theoretical brilliant cut diamond. Those proportions and facet angles calculated mathematically by Marcel Tolkowsky to produce maximum brilliancy consistent with a high degree of fire in a round diamond brilliant are considered by many diamond men to constitute the ideal cut. These figures, computed as a percentage of the girdle diameter, are as follows: total depth, 59.3% (without provision for girdle thickness); crown depth, 16.2%; pavilion depth, 43.1%. The bezel angle is 34° 30’ and the pavilion angle is 40° 45’. Girdle thickness as a percentage of the girdle’s diameter varies with size. The larger the stone, the smaller the percentage for a medium girdle. The variation is from about 1% to 3%.

IGI :
International Gemological Institute - Provides diamond and colored stone grading reports and appraisals. Offices located in New York, Antwerp, and Thailand.

Indented Natural:
A natural that penetrates the stone.

Included:
Clarity grade, referring to eye visible imperfections, existing in I1,I2,I3

Industrial Diamonds:
Non-gem quality diamonds used in drills and other tools.

Internal Reflection:
The reflection of a feature within a stone.

Imperfect:
The diamond imperfection grade at the low end of the “flawless-to-imperfect” (or “perfect-to-imperfect”) scale. An imperfect diamond contains imperfections that are visible face up to the unaided eye or that have a serious effect on the stone’s durability. The Gemological Institute of America recognizes two grades in the imperfect category.

Imperfection:
A general term used to refer to any external blemish or internal inclusion or flaw on or in a fashioned diamond; e.g., a feather, carbon spot, knot, fissure, scratch, natural, etc. The term “flaw” and “imperfection” are usually used interchangeably.

Iridescence:
Prismatic colors inside or on the surface of a material caused by light interference from thin layers of differing refractive indices. These layers may be thin films of liquid, gas or solid. Pearls are best known for exhibiting iridescence.

Illusion setting:
This setting is more intricate than others in that it surrounds the stone to make it appear larger. The metal that surrounds the stone usually has an interesting design. Click here to learn more about jewelry settings.

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