Colour Stone Grading System

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Clarity is also important in coloured gems as they are in diamonds. The standards are quite different though. If you applied the diamond standards to coloured stones, it would result in buyer missing out in quality stones.

When purchasing coloured gems colour is the most important feature of the gem. Inclusions can be tolerated as long as it does not reduce the beauty of the stone. Gemologists require inclusions in a coloured gem in order to certify it as a natural stone.

There is no international standard for grading clarity in colored gems. However, GIA has established a clarity type system for coloured gems to help fellow consumers to understand that there are different clarity standards for different gem varieties.

We begin with the clarity terms of the GIA colored stone grading system. While the terms are somewhat similar to those used in GIA's diamond grading system, it really is like comparing apples to oranges.

  • Eye Clean = approximately equivalent to Flawless grades for diamond
  • Slightly Included = approximately equivalent to VVS/VS
  • Moderately Included = approximately equivalent to SI
  • Heavily Included = approximately equivalent to Included, level 1
  • Severely Included = approximately equivalent to Included, level 2 or 3

 

The GIA system classifies gem varieties according to 3 types:

Generally completely clean
Type 1 gems
Generally eye clean
Type II Gems
Generally eye included
Type III Gems
Beryl
Aquamarine
Golden beryl
Pink beryl

Garnet
most red gems

Quartz
Citrine
Smoky quartz
Pale amethyst

Topaz
Colourless
Blue

Zoisite
Tanzanite
 
Chrysoberyl
Alexandrite

Corundum
Ruby
Sapphire

Garnet
Rhodolite
Tsavorite

Quartz
Amethyst

Peridot

Spinel
Red, Orange, etc.

Topaz
Imperial
Beryl
Emerald
Red Beryl

Tourmaline
Red Tourmaline
Paraiba Tourmaline

Type I gems are usually found virtually inclusion free in the market. High quality specimens of Type 1 gems would have only tiny inclusions that could only be detected under 10x magnification. So when selecting a Type 1 gem, a buyer should expect the gem to be almost loupe clean. Type 1 gems include aquamarine, morganite, yellow beryl, chrysoberyl, kunzite, danburite, smoky quartz, blue topaz, blue zircon, white zircon and tanzanite.

Type II gems are usually found with inclusions and a high quality specimen would be eye clean rather than almost loupe clean as in the case of a Type 1 gem. Type 2 gems include apatite, alexandrite, corundum (ruby and sapphire), diopside, fluorite, garnet, iolite, peridot, most quartz varieties (such as amethyst and ametrine), spinel, most tourmaline colours (with the exception of green, rubellite and watermelon) and red, yellow and orange zircon.

Type III gems are almost always found with significant inclusions. Even high quality specimens will have inclusions that are visible to the naked eye. Type 3 gems include emerald, red beryl, idocrase, benitoite, kyanite, prehnite, sphalerite, sphene and watermelon and rubellite tourmaline.

The GIA clarity grading relates to the Gem Guide scale of 1-10 in the following matrix, as seen in The Gem Guide Color price book, Fall/Winter 2008-2009. p. 7.

  1-2 Lower commercial 3-4 Middle to upper commercial 4-6 Good 6-8 Fine 8-10 Extra fine
Severly Included Heavily Included Moderately Included Slightly Included Eye-clean
Type I Inclusions are prominent and have a severe effect on appearance durability, or both. Inclusions are prominent and have a negative effect on appearance or durability. Minor inclusions somewhat easy to see with the unaided eye. Minute inclusions difficult to see with the unaided eye. The stone appears clean to the unaided eye.
Type II Inclusions are prominent and have a severe effect on appearance, durability, or both. Inclusions are prominent and have a negative effect on appearance or durability. Noticeable inclusions apparent to the unaided eye. Minor inclusions somewhat easy to see with the unaided eye. The stone appears clean to the unaided eye.
Type III Inclusions are prominent and have a severe effect on appearance, durability, or both. Inclusions are prominent and have a negative effect on appearance or durability. Obvious inclusions very apparent to the unaided eye. Noticeable inclusions apparent to the unaided eye. The stone appears clean to the unaided eye.

 

The main differences between grading the clarity types are seen mainly in the Good 4-6 and Fine 6-8 ranges. For example, an aquamarine (type 1) must have only minute inclusions, barely visible with the unaided eye, to be in the Slightly included Fine 6-8 range. Its cousin, the emerald, could have noticeable inclusions apparent to the naked eye and still be considered Slightly included Fine 6-8. All types must be eye clean to be considered Extra Fine 8-10, and all types that are heavily or severely included can be no higher than 3-4.