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Grading Standards

Grading Standards and Gem Quality Information

The 4 – C’s of Gemstones – A stone’s color, clarity, cut and carat weight.  The explanations below are base on the system of evaluation established by the Gemological Institute of America (GIA).  For more information on the GIA, please visit www.gia.edu.

Color: Is typically the most important value-setting factor of gemstones.  All gems have a preferred color or a small range of preferred colors.  The more the color varies from this range the less valuable the stone.  Color is composed of three dimensions:  hue, tone, and saturation.  Hue refers to the impression of color usually noticed immediately, such as red, yellow or green.  Tone refers to the degree of lightness or darkness of an object.  Saturation defines the degree of purity of a hue.

Cut: Cut refers to the shape or design of a stone, arrangement of facets, as well as the overall symmetry or proportions and the degree of finish or polish.  A well-proportioned, meetpoint faceted cut with a superb polish will elicit and take full advantage of the gemstone’s optical properties.

Carat Weight:  Gemstones are weighed in of the metric carat.  The metric carat is equal to 0.2 of a gram.  Although most commonly associated with Diamonds, the metric carat can be further subdivided into hundredths of a carat or in trade language – points.  A quarter of a carat (0.25 ct) is the same as 25 points.

Clarity:  A gemstone’s clarity grade is directly related to its rarity.  Clarity refers to a gemstone’s relative freedom from clarity characteristics.  Clarity characteristics include inclusions (lie within the stone) or blemishes (lie on the surface of the stone).  The fewer clarity characteristics, the rarer the gemstone is. Each variety has its own clarity standards.  For this reason, the GIA’s grading system divides transparent colored gemstones into three clarity types.  This allows the gems to be more evenly evaluated, as it takes into account the individual nature of each gemstone.  Each type is further sub-divided into five grading descriptions.

Clarity Types

Type I gems are often virtually free of clarity characteristics.  The colored gemstones that most commonly exhibit this trait are:  Aquamarine, Green Tourmaline, Tanzanite, Topaz – Blue, and Zircon – Blue.

Type II gems normally contain clarity characteristics.  The gemstones that most commonly exhibit this trait are:  Alexandrite, Amethyst, Ametrine, Citrine, Iolite, Peridot, Ruby, Garnets, Smoky Quartz, Sapphire – All colors, Spinel – All colors, Tourmaline, and Zircon – Green, Orange, Red, and Yellow.

Type III gems almost always contain clarity characteristics.  These include: Emerald and Tourmaline – Watermelon.

Clarity Grades

        Type I: Usually eye-clean with no clarity characteristics visible to the unaided eye.     Type II:  Typically shows some eye-visible clarity characteristics that do not detract form the overall beauty of the gem.     Type III:  Almost always contain eye-visible clarity characteristics.  
  Eye Clean   Appears clean to the unaided eye.   Appears clean to the unaided eye.   Appears clean to the unaided eye.
Slightly Included   Minute inclusions difficult to see with the unaided eye. Minor inclusions somewhat easy to see with the unaided eye.   Noticeable inclusions apparent to the unaided eye.  
Moderately Included Minor inclusions somewhat easy to see with the unaided eye. Noticeable inclusions apparent to the unaided eye.   Obvious inclusions very apparent to the unaided eye.
Heavily Included     Prominent inclusions that have a negative effect on appearance or durability.    
Severely Included Prominent inclusions that have a severe effect on appearance or durability.  


American Gem Trade Association (AGTA) Enhancement Codes and Designations

(Source:  The Gemstone Information Manual by AGTA, Seventh Edition)


Enhancement: Any traditional process other than cutting and polishing that improves the appearance (color/clarity/phenomena), durability, or availability of a gemstone.

N – The “N” symbol appears only for natural stones which are not currently known to be enhanced; however, the N symbol can also be used for other natural gemstones in the event that a gemstone has received no enhancement and the seller will provide a guarantee that there has been none.

E – The “E” symbol indicates that the gemstone has undergone its traditional enhancement process.

Symbols for Specific Form of Enhancement

Bleaching (B):  The use of heat, light, and/or other agents to lighten or remove a gemstone’s color.

Coating (C):  The use of such surface enhancements as lacquering, enameling, inking, foiling, or sputtering of films to improve appearance, provide color, or add other special effects.

Dyeing (D):  The introduction of coloring matter into a gemstone to give it new color, intensify present color or improve color uniformity.

Filling (F):  The filling of surface-breaking cavities or fissures with colorless glass, plastic, solidified borax or similar substances.  This process may improve durability, appearance, and/or add weight.

Heating (H):  The use of heat to effect desired alteration of color, clarity, and/or phenomena. If residue of foreign substances in open fissures is visible under properly illuminated 10X magnification HF should be used.

Heat & Pressure (HP):  The use of heat and pressure combined to effect desired alteration of color, clarity and/or phenomena.

Impregnation (I):  The impregnation of a porous gemstone with a colorless agent (usually plastic) to improve durability and appearance.

Oiling/Resin Infusion (O):  The filling of surface-breaking fissures with colorless oil, wax, resin, or other colorless substances, except glass or plastic, to improve the gemstone’s appearance.

Irradiation (I):  The use of neutrons, gamma rays or beta particles (high energy electrons) to alter a gemstone’s color.  The irradiation may be followed by a heating process.

Diffusion (U):  The use of chemicals in conjunction with high temperatures to produce artificial color and/or asterism-producing inclusions.

Waxing/Oiling (W):  The impregnation of a colorless was, paraffin, and oil in porous opaque or translucent gemstones to improve appearance.

Quality Criteria by Mineral Type

The following list is by no means all inclusive and will be updated as grading standards are revised by generally accepted trade practices.  To the best of Mainely Gems ability, every mineral or material that is purchased will have full disclosure to the Four C’s and any treatments or enhancements from its natural state.

Beryl:

Variety – Morganite

AA:  Eye clean; light to medium light pink; good cut

Variety – Aquamarine

B:         Included; light color; good cut
A:         Slightly included; medium to light color; good cut
AA:      Eye clean; medium color; good cut
AAA:    Eye clean; medium to dark color; good cut

Corundum:

Variety – Ruby

C2:       Commercial quality; included; variation in color
B:         Included; light pinkish red; good cut, good polish
A:         Slightly included; medium pinkish red; good cut, good polish
A+:       Eye clean; medium to medium dark pinkish red; good cut, good polish
AA:      Eye clean; medium dark pinkish red; brilliance; good cut, good polish
AAA:    Eye clean; medium dark pinkish red to red; brilliance; excellent cut and polish

Variety – Blue Sapphire

C2:       Commercial quality; included; variation in color
A:         Slightly included; medium to dark navy; good cut, good polish; little or no color zoning
A+:       Very slightly included; medium navy; good cut, good polish; little or no color zoning
AA:      Eye clean; medium navy to royal blue; brilliance; good cut, good polish
AAA:    Eye clean; medium navy to royal blue; brilliance; excellent cut and polish

Variety – Pink Sapphire

AA:      Eye clean; medium pink; brilliance; good cut and polish; little or no color zoning
AAA:    Eye clean; medium to dark pink; brilliance; excellent cut and polish; little or no color zoning

Variety – Yellow Sapphire

A:         Eye clean; light to medium yellow; brilliance; good cut and good polish
AA:      Eye clean; medium yellow; brilliance; good cut and good polish
AAA:    Eye clean; medium to dark yellow; brilliance; excellent cut and good polish

Garnet:

Variety – Almandite

AA:  Eye clean; medium to dark red to orange brown; good cut

Variety – Rhodolite

AA:  Eye clean; medium to dark raspberry to plum; good cut

Variety – Spessartite

B:       Included; light to medium yellowish orange; good cut
A:      Slightly included; medium light to medium yellowish orange; good cut
AA:    Very slightly included; medium yellowish orange; good cut

Variety – Tsavorite

A:         Eye clean; light to medium light yellowish green; excellent color and polish
AA:      Eye clean; medium slightly yellowish green; excellent color and polish
AAA:    Eye clean; medium to medium dark very slightly yellowish green; excellent color and polish
Gem:   Eye clean; medium dark to dark forest green; top color; top brilliance; excellent cut and polish

Iolite

A:         Eye clean; medium light to medium, grayish purple, grape color; good cut
AA:      Eye clean; medium to dark grayish purple, grape color; good cut
AAA:    Eye clean; very dark to vivid grayish purple, grape color; good cut

Peridot

AA:  Eye clean; medium to dark, yellowish green; good cut

Opal:

Variety – Black

A:         Semi-Translucent to opaque background; good to medium play-of-color; blues, greens, and reds.
AA:      Translucent to opaque background; medium to strong play-of-color; blues, greens, and reds.
AAA:    Translucent to opaque background; vibrant play-of-colors; blues, greens, and reds.

Variety – Mexican Fire

AA:      Clean; medium to dark orange – reddish orange; good faceted cut
AAA:    (Cheery) Clean; medium to dark orangey red; good faceted cut

Variety – White

A:         White background; good to medium play-of-color; blues, greens, and reds.
AAA:    White background; medium to strong play-of-color; blues, greens, and reds.

Quartz:

Variety – Amethyst

B:         Eye clean to slight imperfections; light purple; little or no color zoning
A:         Eye clean to slight imperfections; light to medium purple; little or no color zoning; good cut
A+:       Eye clean to slight imperfections; medium purple; little or no color zoning; good cut
AA:      Eye clean to slight imperfections; medium/dark purple; little or no color zoning; good cut
AAA:    Eye clean to slight imperfections; deep purple; little or no color zoning; good cut

Variety – Ametrine

A:         Eye clean; light purple and light golden yellow; little or no color zoning
AA:      Eye clean; medium light purple and medium light golden yellow; little or no color zoning; good cut

Variety – Citrine

A:         Eye clean; light, slightly golden yellow; little or no color zoning; good cut
AA:      Eye clean; medium golden to slightly orange; little or no color zoning; good cut
AAA:    Eye clean; medium golden to yellowish orange; little or no color zoning; good cut

Variety – Rock or Clear

A:         Eye clean; nearly colorless; good cut
AA:      Eye clean; nearly colorless to colorless; good cut and polish
AAA:    Eye clean; colorless; excellent cut and polish

Variety – Rose

A:         Eye clean to slight imperfections; milky; light to medium pink; color zoning; good cut
AA:      Eye clean to slight imperfections; milky; medium to deeper pink; minor color zoning; good cut
AAA:    Eye clean to slight imperfections; milky; deep pink; little or no color zoning; excellent cut and polish

Variety – Smoky

A:         Eye clean; light, slightly tan to medium-light tan; good cut
AA:      Eye clean; medium-light tan to medium-dark brown; good cut
AAA:    Eye clean; medium-dark brown to dark brown; excellent cut and polish

Tanzanite

B:         Very slightly included; medium light bluish purple; brilliance; good cut and polish; little or no color zoning
A:         Eye clean; medium light bluish purple; brilliance; good cut and polish; little or no color zoning
AA:      Eye clean; medium bluish purple; brilliance; good cut and polish; little or no color zoning
AAA:    Clean; medium dark bluish purple; brilliance; good cut and polish; no color zoning
Gem:   Clean; vibrant, medium dark purple; brilliance; excellent cut and polish; no color zoning

Topaz

Variety - Blue

AA:      Sky; Eye clean; bright light blue; good cut and polish
AA:      Swiss; Eye clean; medium to dark, bright blue; brilliance; good cut and polish
AA:      London; Eye clean; medium dark grayish blue; brilliance; good cut and polish

Variety - Precious

A:         Eye clean; light golden color; good cut
AA:      Eye clean; light to medium golden to slight peach; good cut
AAA:    Eye clean; medium to strong golden with peach tones; good cut
AAA:    Imperial; Eye clean; peach to pink color; good cut

Tourmaline

Variety – Chrome (Green)

A:         Eye clean to slight imperfections; medium to dark yellowish green; good cut
AA:      Eye clean to slight imperfections; medium yellowish green; good cut
AAA:    Eye clean to slight imperfections; light to medium yellowish green; good cut

Variety – Indicolite (Dark Violetish Blue, blue, and greenish blue)

B:         Included; medium to dark violetish blue or blue or greenish blue; good cut
A:         Eye clean to slight imperfections; medium to dark violetish blue or blue or greenish blue; good cut
AA:      Eye clean to slight imperfections; medium violetish blue or blue or greenish blue; good cut
AAA:    Eye clean to slight imperfections; light to medium violetish blue or blue or greenish blue; good cut

Variety – Parti-Colored (More than one color)

B:         Included; light green and light pink color; good cut
A:         Eye clean to slight imperfections; light green and light pink; good cut
AA:      Eye clean to slight imperfections; medium green and medium pink; good cut

Variety – Pink

AA:      Eye clean; medium color; bright pink; good cut

Variety – Rubellite

AA:      Eye clean; medium color; bright Red, Purplish Red, Orangey Red, or Brownish Red; good cut

Zircon

Variety – Blue

AA:      Eye clean; medium dark, slightly greenish blue; good cut and polish

Variety – White

AA:      Eye clean; near colorless; good cut and polish      

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