PRECIOUS COLORED GEMS
A gemstone is the crystalline form of a naturally occurring mineral that is desirable for its beauty, valuable due to its rarity and durable to be worn for many years.
Typically, colored gems are categorized as precious and semi-precious. The precious gems include rubies, emeralds, sapphires, diamonds and pearls. The remaining gems are placed in the semi-precious group. Today, the line of delineation between precious and semi-precious is not as sharply defined and other rare gems, like alexandrite, are included in the precious gem class.
Sapphire comes from the mineral corundum when its color is anything except red or deep pink, in which case it is considered to be a ruby. Elements such as iron, titanium, or chromium in negligible amounts can give corundum blue, yellow, pink, purple, orange, or greenish color. Pink-orange sapphires are called Padparadscha. Blue, though, is the most well-known hue.
Hue, saturation, and tone are the three components of color. The “color” of the gemstone is its hue. Saturation refers to the vividness or brightness of the hue, and tone is the lightness to darkness of the hue. Blue sapphires are evaluated based upon the purity of their primary hue followed by the secondary hue that is usually purple, violet, and green. Violet and purple can positively contribute to the color’s beauty, while green detracts. Blue sapphires with a little violet or purple are generally said to be of fine quality. Blue sapphires with green as a secondary hue are not considered to be as good a quality. Gray is the normal saturation modifier or mask found in blue sapphires. Gray reduces the saturation or brightness of the hue and therefore has a negative effect.
Sapphires register a 9 on the Mohs hardness scale of 1 to 10, where diamond is 10. It is a very good gemstone choice for jewelry due to its hardness. Historically, some of the best known sapphires were mined in Kashmir, its color described as a “cornflower blue”. Due to different reasons, sapphires are not available from Kashmir. Burma was also a very good source for high quality sapphires and rubies, until its political strife closed the production. Currently, many of the finest sapphires are being mined from Sri Lanka—although other locations include Thailand, Madagascar, Australia and others.
A star sapphire is a type of sapphire that exhibits a star-like phenomenon known as an asterism. The asterism looks like a six-rayed “star”-shaped pattern when viewed with an overhead light source.
Sapphires may be treated by a few different methods. It is customary to heat natural sapphire to improve or enhance color. Evidence of sapphire and other gemstones being subjected to heating may go as far back as to Roman times. Unheated gems are very rare and typically accompanied by an independent gem laboratory certificates attesting to “no evidence of heat treatment”. Other methods that are not customary are diffusion treatments that add elements to sapphires to change its color. According to the Federal Trade Commission guidelines in the United States, disclosure of any treatment is required.
The ruby, a type of mineral corundum, is a blood-red colored gemstone. The red color is caused mainly by the presence of the element chromium. Burma was the world’s main source for rubies for hundreds of years. Some of the finest rubies were mined from the Mogok Valley. Its best color has been described as “pigeon’s-blood”. Rubies are mined in other countries like Thailand, Cambodia, Vietnam and more recently Kenya to name some. Other kinds of the gem-quality corundum are known as sapphires.
Prices of rubies are determined by color, clarity, cut, and carat weight. The brightest and most valuable “red” called pigeon blood-red, demands the highest value over other rubies of similar quality. The clearer the clarity, the better a ruby it is. A well-proportioned and lively cut is a more desirable gem than one not cut well and “sleepy”. Ruby is commonly available in sizes up to 2-3cts, but larger high quality gems are genuinely very rare.
After diamonds that possess a Mohs hardness of 10.0, rubies have a hardness of 9.0. All rubies have imperfections in them including color impurities and types of inclusions known as “silk”. Customarily, the rough stone is heated before cutting to attain its final color.
Rubies that are not heated but still have an exceptional quality of color, clarity and cut, command a large premium. Other forms of color treatment may be performed and must be disclosed to the purchaser.
Emeralds come from the mineral beryl and derive their color by trace amounts of chromium. It has a hardness that ranges from 7.5-8.0 on the 10 point Mohs scale of hardness. The more inclusions in an emerald the less resistant it is to breakage. Emeralds come from Columbia, Brazil, Zambia and other countries.
A fine emerald should have a verdant green color and a high level of transparency. Emeralds occur in hues ranging from yellow-green to blue-green, with green being the primary color. Only gems that are medium to dark in tone are considered emerald. Lighter tones are known as green beryl. The hue should also be vivid. Emeralds are known to have many inclusions. Therefore, it is not graded with a 10X magnification like diamonds, but with an unaided eye. If the emerald has no visible inclusions to the eye it is considered “very clean”. Almost all emeralds are “oiled”, a treatment used to enhance its clarity. Cedar oil, having a similar refractive index, is customarily used in this generally accepted practice. Other synthetic oils and polymers may also be used. The U.S. Federal Trade Commission requires the disclosure of a treatment when a treated emerald is sold. The customer should be cautioned to inquire about the extent of treatments on each emerald to facilitate making appropriate comparisons among gems being considered.
A reputable jeweler, like
, iis available to describe the various qualities of gemstones and disclose pertinent information for the customer to make an educated choice.