The various gem categories used at Hannoush Jewelers (i.e. Precious and Semi Precious,  are standard classifications based on value and rarity. For example, Precious Gems include those varieties (e.g. Emerald, Ruby etc.) with high market values.  Semi Precious Gems generally includes everything else that is mainstream.

Color

Color is the single most important factor when evaluating colored gems. Basically, the more attractive the color seen, the higher the value. Bright, rich and intense colors are valued over those that are too dark or light. Colors that are dulled by tones of black, gray or brown are regarded as less desirable. The colors seen should ideally remain attractive regardless of prevailing light conditions. Whether viewed indoors, outdoors, by day or by night, a gem should always remain beautiful.

The mixing of color hues into combinations, such as purple-blue in Tanzanite and bright blue-green in Apatite is attractive and value enhancing. Although specific colors hues can affect the prices of gems, personal preferences are also very important.

Many gems also have specific expressions to denote the very top colors found within a species. For example, Pigeon Blood Red or Cornflower Blue are respectively used for Ruby and Sapphire. Such terms are equable with the most desirable colors to be found within a gem species (i.e. colors that cannot be bettered).

Optical Effects

Some gems exhibit unusual optical effects known as phenomena. These rare and beautiful effects very often add value to gems. The Cat’s Eye Effect, the Star Effect and the Color Change Effect are very popular phenomena and are highly valued.



Chatoyancy
Chatoyancy or the Cat’s Eye Effect is a reflection effect that appears as a single bright band of light across the surface of a gemstone. This phenomenon is commonly found in Chrysoberyl, Tourmaline and Tigers Eye.
 

Asterism
Asterism or the Star Effect is a reflection effect that appears as two or more intersecting bands of light across the surface of a gem. This phenomenon is commonly found in Ruby, Sapphire and Garnet.
 

Color Change
Color change gems are those that distinctly change their color when viewed under two different light sources. This phenomenon is commonly found in Alexandrite, Sapphire and Color Change Garnet.
 

Iridescence
Iridescence is the rainbow like color effects seen in some gems. This phenomenon is commonly found in Opal, Ammonite and Moonstone.
 

Aventurescence
Aventurescent gems are those that have a colorful play of glittering reflections from small metallic inclusions. This phenomenon is commonly found in Sunstone, Aventurine Quartz and Gold Stone.



Cut & Polish

Unlike Diamonds, colored gems possess variable optical properties and are not cut to a uniform ideal. A well-cut colored gem exhibits even color, a minimal number of inclusions, good brilliance and shows the majority of Carat weight when viewed from the top. A well-cut gem should also exhibit good symmetry and polish condition. Facets should be aligned straight in relation to the gem’s girdle and also to each other. Polish condition should be good with no visible surface pits and polishing lines.


Table

Girdle
Crown

Pavillion

Culet
(may or may not be faceted)

Industry Standard Anatomic Layout Of A Faceted Gemstone
 

	Table
Girdle		Crown
		Pavilion
	Culet (may or may not be faceted)
Industry Standard Anatomic Layout Of A Faceted Gemstone

Broadly, the styles of gem cutting can be divided into Faceted Gems (gems with geometrically shaped flat polished faces) and Non-Faceted Gems (those Gems that do not have geometrically shaped flat polished faces such as cabochons).

Antique Cushion	Baguette	Emerald Cut	Briolette
Heart Cut			Octagon Cut
Pear Cut	Common Cuts		Marquise Cut
Round Brilliant Cut			Oval Cut
Square Cut	Trilliant Cut	Round Cabochon	Princess Cut

Carat Weight

Gemstone weight is measured in Carats. This unit of measurement originates from the traditional use of carob seeds to weigh gems. Carob seed were used because of their consistent size and shape. One Carat is the equivalent of 0.20 Grams. Further divided into 100 smaller units known as Points, the term carats is often confused with “Karats”. “Karat” is a measurement of gold purity and has no relationship to the term Carats.

As the weight of a gem increases, so does its price per Carat. Large gems are always rarer than smaller ones, so per Carat prices rise exponentially. A 3 Carat Ruby is always worth far more than three 1 Carat Rubies of the same quality.

Gemstone prices also increase rapidly when in excess of certain key weights. For example, a 2.01 Carat Ruby has a higher price tag than a 1.99 Carat Ruby, despite a negligible difference in actual size. Pricing is said to suffer a “Non Linear Scale of Increments”.

Clarity

Most gems contain tiny natural features called inclusions. Mostly microscopic in nature, they are most easily glimpsed under magnification. Inclusions that don’t interfere with the brilliance, sparkle and fire of a gem don’t affect the value.

Many gems have tendencies to be more included than other varieties. For example, Emeralds are known to be far more included than Sapphires and this should be taken into account when making your selection.

The clarity of gems is determined by judging the amount and location of inclusions seen. Basically, the higher the clarity grade, the higher the value of the gem.
Durability

Gems with better durability and resistance to wear are generally more highly prized than those of lesser durability.

Rarity




Generally, rare gems are more highly prized than more common varieties. However, if a gem variety is so rare that it is essentially unknown to the general public, it is often classified as a "collector gem". Gems such as Boracite, Childrenite and Simpsonite are extremely rare, attractive and durable, but they are unlikely to command prices appropriate to their rarity because fewer people are aware of their existence.

Historical Connotations

Species of gems that are rich in history and lore are more highly prized by some individuals than those lacking a rich lore or history. A good example of this is Rubies from the Mogok Valley in Burma. While many people are prepared to pay considerably more for Rubies from Mogok, other individuals may feel that a comparable Ruby from Madagascar will be better value.

Pairs & Suites

Pairs or suites of gems matched for color, clarity and cut are valued more highly per Carat or per gem than single gems of the same quality. Given the rarity of many gems, a matching set is disproportionately hard to find and will command a higher per Carat price than if each of the gems from the suite were sold separately.

Gemstone Treatments

For some people, gems that have not been enhanced in color or clarity by heating or other methods are sometimes worth more. For other people, enhancements are a godsend, as they make expensive gems far more affordable. Click here to learn about globally accepted gemstone treatments.