Let’s embark on a journey into the world of colour and discover what factors make a gem rare and valuable. Like a diamond, the combinations of a gemstone’s colour, cut, carat weight and clarity determine its rarity. Below is a guide that will assist you in understanding the 4 C’s of Gemstones.


Typically, colour is the most important factor in determining the value of gemstones. All gems have an ideal colour or a relatively small range of ideal colours. The more the colour varies from this range, the less valuable the stone. Colour is composed of three dimensions: hue, tone and saturation. Hue refers to the colour usually noticed immediately, such as red, green or blue. Tone refers to the degree of lightness or darkness and saturation defines the level of purity of the hue.


Cut refers to the shape of a stone, the arrangement of facets as well as the accuracy of the proportions and finish. The beauty of a gemstone is revealed in the cutting process. Gemstones can be carved into almost any shape imaginable, but are traditionally cut into familiar shapes, such as oval, emerald, pear, round and marquise. Proportions involve the balance and appeal of the basic shape while finish refers to the detail of the workmanship. A cut that is well proportioned with an excellent finish will show a stone’s properties to its fullest potential. When all other factors are in balance, i.e. colour, clarity and carat weight, a better-cut gem will be more valuable.

Carat Weight

A gemstone is measured by its weight and not by its dimensions. One carat, the traditional unit of measurement, is equal to approximately 0.2 grams. The weight of a gemstone may also be referred to in points. Two different gemstones may have the same dimensions but different weights. This is due to the specific density of the gem mineral and can assist gemologists in identifying a gemstone. To a certain point, the larger the gemstone, the more rare it is and, thus, commanding a higher price. Some stones commonly occur in larger sizes, the value of which may decrease if the size of the gemstone is impractical for jewellery use.


Clarity refers to the number and position of inclusions present in the gemstone and is directly related to its rarity. Clarity characteristics consist of inclusions which occur internally within the stone, or blemishes which occur on the surface of a stone. Each variety of gemstone has its own clarity standards, eg: Tanzanite is virtually inclusion-free, while Emerald almost always contains inclusions. For this reason, the grading system for coloured gemstones is divided into three clarity types. This process allows the gemstones to be more equally evaluated as it takes into account the individual nature of each gemstone. The table below shows how each Type is then further divided into five grading descriptions.

  • Type I: gemstones are generally free of clarity characteristics and commonly include Green Tourmaline, Tanzanite, Blue Topaz and Blue Zircon.
  • Type II: gemstones normally contain clarity characteristics and commonly include Alexandrite, Garnet, Smoky Quartz, Green Zircon, Amethyst, All Colours of Sapphire, Orange Zircon and Lolite.
  • Type III: gemstones almost always contain clarity characteristics and include Emerald and Tourmaline.


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 from 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.
Minute inclusions difficult 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, durability, or both.


The combinations of color, clarity, cut and carat weight are primary factors in determining the value of a gemstone. Other factors that affect rarity are the geographic location where the gemstone is mined as well as the abundance of a particular stone. Some gemstones are more easily accessible while others found in remote locations make mining nearly impossible.

Gemstones are beautiful, rare and valuable treasures – enjoy!

**Note: The information and explanations in this tutorial are sourced from the Gemological Institute of America (GIA). For more information on the GIA, please visit