Gem Education

The term "gemstone" describes any of the hundred naturally-occurring minerals (diamond, ruby, sapphire, etc.) and organic materials (amber, pearls, etc.) that are used for personal adornment or display. However, the majority of the popular gem materials seen today are inorganic.

To be classified as a gemstone, an organic or inorganic material must have beauty, rarity, and durability. A gem’s beauty comes from its brilliance, fire, luster and color. In their rough form these attributes are often masked, after cutting and faceting and often other enhancements, can the true beauty of the mineral/gemstone be revealed. Durability refers to a combination of the material’s hardness (ability to withstand scratching), toughness (ability to resist breakage), and stability (ability to withstand chemical or physical change resulting from heat, light or chemical exposure).

There are approximately 2,700 different minerals on record, however, less than one hundred are regarded as a gemstone or ornamental variety for jewelry use and less than 50 are regarded as common. Gems are grouped by their composition and classed by species and variety.

Value Factors


The single most important factor to a gemstone is color. Some colore-stone experts estimate that the color of a gemstone accounts for 50% to 70% of the gemstones value. Gemologists consider a gem’s body color in terms of hue, tone and saturation. Combinations of these properties help create the colors we observe.

- Hue is the base color that first stands out when viewing a gemstone. For example, blue, violet, purple, red, orange, green and yellow are all hues.

- Tone describes the degree of lightness or darkness of a color. For example, a red stone can be dark red, medium red or light red. There are 11 positions ranging from colorless to black (black and white are not considered hues, because they are the extremes of the tonal scale) on the GIA tone scale.

- Saturation refers to the degree of intensity of a color. The GIA saturation scale groups hues into cool hues, (including blue and violet) and warm hues (including orange and red). Cool hues can look grayish as their saturation of color decreases, while warm hues can look brown as their saturation level decreases. There are six degrees of saturation on the GIA saturation scale. These range from grayish (in the cool hues) or brownish (in the warm hues) to vivid. Desirable saturation levels for most gems fall in the moderately strong, strong or vivid range.


Clarity refers to the degree to which a transparent gemstone is free of internal or surface imperfections. Internal imperfections are commonly referred to as inclusions and external imperfections are commonly referred to as blemishes in the gem trade. The types of inclusions encountered in gems include needles (mineral fibers that formed during crystallization), crystals (small mineral crystals of the same or different type as the gem that formed in the host), pinpoints (tiny crystals), feathers (natural separation across an atomic plane), fingerprints (a healed or partially healed break in the gem), color zoning, chips, scratches, etc. Inclusions are not necessarily a negative feature to a gem. Certain gems cannot exist without them. Gemologists consider the type, size, number and position of inclusions when considering clarity.


The cut of a gemstone refers not to shape of the stone (round, pear etc.), but to how well the proportions, symmetry and polish are executed. How a gem is cut can affect the overall value because of its influence on color. Well-cut stones bring out the beauty and brilliance more, therefore increasing the overall grade. There are many factors to consider when valuing the cut of a gemstone. Brilliance, windowing, extinction, polish and symmetry are all factors that should not be overlooked.

- Brilliance refers to how bright or glittery a gem is.

- Windowing refers to the washed-out area of body color in a gem. If there is a large degree of windowing in a gem, you can usually read text placed underneath the stone when the stone is placed in contact with the text (such as magazine print). Windowing occurs when gemstones are cut too shallow.

- Extinction refers to dark areas in the stone. Extinction occurs in stones that are cut too deep or have significant pavilion bulge (rounding of the pavilion).

- Polish and Symmetry refer to how sharply and well defined the relationship is between the crown and the pavilion. When care is taken, all facets will be polished well and the arrangement will align the facets properly for the shape of the gemstone.