Colored gemstones are among the most popular center and accent stones for jewelry items. Here, we present the basics of colored gemstones.
While there are no official 4 C's for grading colored gemstones, like there are with diamonds, many of the same principals apply. Following are the 4 C's as they apply to colored gemstones:
Clarity in most gemstones does not influence its value or beauty unless it breaks the surface or affects the integrity of the gemstone. In lighter colored stones, clarity may be more important than in darker stones that can mask imperfections. However, flawlessness in colored gems is even more rare than in diamonds.
The four flaws that occur in gemstones are fault, fissure, fracture and gas bubbles.
It is the type and location of a flaw that is more important than the fact that there is a flaw, since some flaws can affect the stone's durability. Some stones are typically eye-clean such as topaz, while others are expected to have inclusions, such as emerald.
Color has the greatest impact on value. The color should be pure, vibrant, even and fully saturated without being too dark or too light.
Cut affects the amount of brilliance the gemstone returns to the eye, the depth of color seen and the size of the stone. Well-cut gemstones will enhance the color of a stone, while poorly cut gemstones can turn out looking dead and lifeless.
Carat weight determines value in two ways. First, the carat weight x price per carat = total price for the stone. Second, the rarity of the size of stone compared to the normal size found will affect price.
Many gemstones have historically and traditionally been enhanced before bringing them to the customer. Most enhancements have been around for a very long time, some for hundreds of years or longer. The result is an improvement on nature's beauty. It makes gems available and affordable. Most of these enhancements are stable and no special care is required.
Gems that are not usually treated include alexandrite, black star sapphire, cat's eye chrysoberyl, garnets, hematite, iolite, moonstone, peridot, spinel and chalcedonies such as bloodstone, fire agate, onyx and sardonyx.
Hardness vs. Toughness
Hardness describes a material's resistance to scratching. Mineral hardness is measured using the Mohs' scale. The higher the number, the harder the mineral is to scratch. The scale goes up incrementally from 1 until it reaches 9. The difference from 9 to 10 is greater than the difference from 1 to 9. For example, a diamond which is a 10, is 100 times harder than a sapphire or ruby which receive a 9 hardness.
Toughness refers to how easily a gemstone will chip, crack or cleave. Ratings range from poor to excellent. An emerald receives a poor toughness due to internal fractures which make emeralds prone to chipping and cracking. However, rubies and sapphires receive very good to excellent ratings.
Specific Colored Gemstones
Many colored gemstones are also recognized as "birthstones," with one popularly and historically associated with each of the twelve calendar months. Learn more about each: