Buying a gemstone can be a daunting task. It is an experience that requires trust, not only of our senses in judging what we can discern about the gem one is considering, but also the representations of the person selling the gem. Many factors set value. Some of them like weight are tangible; others like clarity, color or origin are not. Gemstones may be accompanied by a lab report listing the color, cut, clarity and weight. They may also contain a comment about treatments or origin. Certain gemstones such as ruby or sapphire can receive a premium in the market if they are believed to be from a particular country (origin). In lieu of an independent grading report, the seller may offer certain guarantees.
Consumers must reconcile their budget with their tastes. A smaller gem of finer quality will cost as much or more than a larger gem of lesser quality. Nature produces far fewer of the top quality gems, so there is good reason for the greater price. The following is a summary of factors for some of the most popular gems in the trade.
Ruby is generally considered the most valuable of the colored gemstones when priced per carat for exceptional quality gems. It is considered one of the “big three” in the industry ruby, emerald, sapphire. Color: Rubies vary in color from orangy red, red slightly purplish red, strongly purplish red, to red. Clarity: Type II May be eye clean with minor inclusions visible under magnification. Cut: Some native cuts may be found (gems cut at the mine location without high regard to skill in cutting). However, well-cut stones are available. Carat weight: Stones weighing more than 5 carats in finer qualities are very rare. In commercial grades, stones are available from in all sizes up to 10 carats. Reference Data: Refractive Index: 1.762-1.770, Specific Gravity: 4.00 Common Treatments: Most rubies are heat treated to improve color. Some may also be heated in the presence of flux which can leave residue within the ruby, known as flux healing. Another method of filling fissures uses lead glass and leaves this residue inside the gemstone.
Emerald is one of the most valuable gems, prized throughout history. It is considered one of the “big three” in the industry – ruby, emerald, sapphire. Color: Very strongly bluish green, bluish green, very slightly bluish green, green and slightly yellowish green. Clarity: Type III usually has eye visible inclusions. Cut: Some native cuts may be found (gems cut at the mine location without high regard to skill in cutting). However, well-cut stones are available. Carat weight: Stones weighing more than 8 carats are rare in finer quality. In commercial qualities, stones are available in all sizes up to 20 carats or even larger may be encountered. Reference Data: Refractive Index: 1.577-1.583, Specific Gravity: 2.72 Common Treatments: Nearly all emeralds are oiled with a variety of oils, some with resins added. Filling of emeralds may also take place. These treatments help to hide the natural fissures within emeralds which is a common feature of their growth in nature.
Sapphire is the most popular gemstone in the United States. It is considered one of the “big three” in the industry – ruby, emerald, sapphire. Color: Sapphires can be found in a variety of colors in each of the seven primary hues. However, blue is the most common, most desired, and most expensive. Clarity: Type IIâ€”May be eye clean with minor inclusions visible under magnification. Cut: Some native cuts may be found (gems cut at the mine location without high regard to skill in cutting). However, well-cut stones are available. Carat weight: Stones weighing more than 20 carats is rare in finer qualities. In lower grades very large sizes are available. Reference Data: Refractive Index: 1.762-1.770, Specific Gravity: 4.00 Treatment: Heat is very commonly used to improve the color of sapphires.
Tanzanite is a very popular variety of zoisite. It gained popularity in the 1970s when Tiffany & Co. brought it to market. Color: Purple, bluish purple, violet, bluish violet, violetish blue and blue. Tanzanite is highly trichroic meaning it exhibits different colors when viewed in different directions. How it is cut by the cutter will also affect what color results in the finished gem. Clarity: Type Iâ€”Usually eye clean with high clarity under magnification. Cut: Well cut stones are expected. Carat weight: Stones weighing up to 20 carats are available in finer qualities and up to 50 carats are available but rare. Reference Data: Refractive Index: 1.691-1.70, Specific Gravity: 3.35 Treatment: All tanzanite are heated to obtain the color.
Commonly Recognized Birthstones
December: Zircon (now tanzanite on some lists)