Unlike with Diamonds, there is no official grading for colored gemstones. However, many of the same principles apply. Before you make a purchase it’s important to have a general understanding of gemstones and the 4 C’s.

Color:
Color is arguably the single most important factor when making your purchase decision. The color of the gem should be vivid, even and fully saturated throughout the entire stone. In general terms, the more attractive the color looks, the higher the value is.

Many gem types also have a mix of color hues that make them even more attractive and valuable. Examples are purple-blue Tanzanite and blue-green Apatite.

In some gems you will see an unusual optical effect known as phenomena. These effects often add value to the gems and include the star effect (often found in Sapphires and Rubies), cat’s eye effect (often found in Tourmaline, Chrysoberyl and Tigers Eye) and color change effect (often found in Sapphire, Garnet and Alexandrite).

Cut:  
The cut of colored gemstones does not affect its value to the same extent as it does with Diamonds. A well cut colored gemstone should exhibit even color, good brilliance, minimal number of inclusions and should show the majority of the carat weight when viewed from the top. A gemstone with good color will only be further enhanced by a good cut. A poorly cut colored gemstone can easily turn out dull and lifeless.

You can divide the styles of gem cut into Faceted and Non-Faceted gems. There are 15 gemstone cuts that are commonly used.

Carat Weight:
As with diamonds, weight in colored gems is measured in Carats. The term Carat comes from the traditional use of carob seeds to weigh gems. Carob seeds were used because of their consistent size and shape. 1 carat is equal to 0.2 grams, so 5 carat is equal to 1 gram. Carat is also divided into points where 1 carat is equal to 100 points.

The price of a gem increases exponentially as the weight increase. For example, a 5 carat Sapphire is always worth much more than five 1 carat Sapphires of the same quality.

Clarity:
In some gems you will see tiny features called inclusions. The clarity of a gemstone is determined by judging the amount of inclusions seen. In essence, the higher the clarity grade, the higher the value of the gem.

However, in some gem types such as Ruby and Emerald inclusions are generally regarded as part of the gemstones character and don’t necessarily decrease the value.

Below is a list definitions Gems Heaven use to describe clarity in gemstones:
 

Gemstone Treatment
Moh's Scale of Hardness