Gemstone Enhancement: How to assess gemstones

The term enhancement is defined as any treatment or process other than cutting and polishing that improves the appearance (color/clarity/phenomena), durability, value or availability of a gemstone. In today’s gem marketplace, many gemstones have been enhanced by a variety of methods. Such processes may range from simple heating (such as with tanzanite) to high-tech irradiation (such as blue topaz). 
At the Collector, we take enhancement disclosure seriously and guarantee, to the best of our abilities, to provide our customers with complete information on any and all enhancements to which a gem has been subjected. While many enhancements are currently undetectable, we do our best to provide all the information you need for informed buying decisions. 
The guidelines we follow are those of the AGTA and are the most stringent in the industry. In addition, we have modified these guidelines slightly in areas where we feel they are not stringent enough (example: flux healing of ruby).
Some gemstone enhancements are less stable than others, meaning that the appearance of a gem may change with time. It is the general policy of the Collector to sell only those gemstones whose enhancements (if any) have good to excellentstability. In the event that we offer a gem with less than good stability, we will ensure you are aware of the special care needed for that stone. A gemstone enhancement is considered stable as long as the gem does not change in appearance (color and/or clarity) under normal wear, cutting, cleaning, repair or display conditions. Gemstones can be divided into three basic enhancement categories.

• Not Enhanced (N)
  The “N” symbol is used on our invoices to indicate one of two situations. First, there are certain gemstones that are not currently known to be enhanced (alexandrite, some garnets, etc.). Second, the “N” symbol may also be used for a gem where it can be proved via gemological or other means that a gem has not been subjected to any enhancement. When you see the “N” symbol on our invoice, we guarantee that the gem in question is unenhanced.
  
• Normally Enhanced (E)
  The “E” symbol is used for gemstones that are routinely enhanced. Since many enhancements are difficult or impractical to prove definitively, unless otherwise indicated, our approach is to assume that such enhancements have been applied to that particular gemstone. This assumption is made to protect both buyer and seller. If a more specific method of enhancement is known, then the specific enhancement code will be used.
  
• Nontraditional Enhancements (T)
  For gemstones not covered by the “N” and “E” symbols, a code covering the specific gemstone enhancement will be listed.

Symbols For Specific Forms of Enhancement

• B = Bleaching: The use of heat, light and/or chemicals or other agents to lighten or remove a gemstone's color. This is often accompanied by subsequent dying and/or impregnation. Example: bleached cultured pearl; bleached/impregnated jadeite (‘B-jade’)
• C = Coating: The use of such surface enhancements as lacquering, enameling, inking, foiling, or sputtering of films to improve appearance, provide color or add other special effects. Example: coated diamond
• D = Dyeing (staining): The introduction of coloring matter into a gemstone to give it new color, intensify existing color or improve color uniformity. Example: dyed green jadeite
• F = Filling: The filling of surface-breaking cavities or fissures with colorless glass, plastic, or some similar substance. This process will improve durability, appearance and/or add weight. Example: ruby
• Fh = Flux healing: During heat enhancement, fluxes (or heat alone) may be used to heal fractures/fissures which were formerly open. The process dissolves the walls of the fractures and redeposits the molten gem material, healing the fractures closed. Example: ruby (particularly that from Möng Hsu, Burma)
• H = Heating: The use of heat to alter color, clarity, and/or phenomena. Example: Ruby, sapphire, tanzanite, aquamarine, demantoid garnet
• I = Impregnation: The impregnation of a porous gemstone with a colorless agent (usually plastic) to give it durability and improve appearance. Example: Stabilized turquoise
• L = Lasering: The use of a laser and chemicals to reach and alter inclusions. Example: diamond
• O = Oiling/Resin Infusion: The filling of surface-breaking fissures with a colorless oil, wax, resin or other colorless substances, except glass or plastic, to improve the gemstone’s appearance. Example: emerald
• R = Irradiation: The use of neutrons, gamma, ultraviolet and/or electron bombardment to alter a gemstone’s color. The irradiation may be followed by a heating process Example: blue topaz
• U = Lattice (‘bulk’ or ‘surface’) Diffusion: Outside-in diffusion of coloring chemicals via high-temperature heat treatment to produce color and/or asterism. Example: lattice diffusion-treated sapphire
• W = Waxing/Oiling: The impregnation of a colorless wax, paraffin and/or oil in porous gemstones to improve appearance. Example: jadeite

Natural Gemstone Enhancement Chart
(based on the AGTA Source Directory 2000–2001)

Natural Gemstone	Enhancement Symbol	Description Used	Frequency Encountered	Stability	Care Requirements
Agate	D	–	Usually	Excellent to good	Normal
Fire Agate	N	–	–	–	Normal
Alexandrite	N	–	–	–	Normal
Amber	E or H	–	Usually	Very good to good	*Special
	D	–	Rarely	Variable	Special
Amethyst	E or H	–	Occasionally	Excellent	*Special
Ametrine	N	–	–	–	Normal
Andalusite	N	–	–	–	Normal
Aquamarine	E or H	–	Usually	Excellent	Normal
Beryl	R	Maxixe	Always	Poor	X-Special
	R	Yellow	Usually	Variable	Special
	N	Yellow-green	–	–	Normal
	E or O	Red	Commonly	Very good to fair	Special
Chalcedony	D	Black	Always	Excellent to good	Normal
	D	Banded	Usually	Excellent	Normal
	D	Green	Usually	Good to fair	Special
	D	Blue	Commonly	Good to fair	Special
	E or H	Carnelian	Usually	Excellent	Normal
	D	Carnelian	Occasionally	Excellent to good	*Special
	D	Jasper	Occasionally	Excellent	Normal
	N	Chrysoprase	–	–	Normal
Chrysoberyl	N	Transparent	–	–	Normal
	R	Cat’s eye	Occasionally	Excellent	Normal
Citrine	E or H	–	Usually	Excellent	Normal
Coral	N	Black	–	–	*Special
	E or B	White	Commonly	Good	Special
	E or W	Pink	Commonly	Good	Special
	I	Orange	Commonly	Good	Special
	B	Gold	Usually	Very good	Special
	D	Red	Occasionally	Variable	X-Special
Natural Gemstone	Enhancement Symbol	Description Used	Frequency Encountered	Stability	Care Requirements
Diamond	L	–	Occasionally	Very good	Normal
	C	–	Rarely	Very good to poor	Special
	F	–	Occasionally	Very good	Special
	HP	–	Rarely	Unknown	Special
Diamond – Fancy	R	–	Occasionally	Excellent to very good	Special
	L	–	Occasionally	Very good	Normal
	F	–	Rarely	Very good	Special
	C	–	Rarely	Fair to poor	Normal
	H	–	Rarely	Unknown	Normal
Diopside – Chrome	N	–	–	–	*Special
Emerald	E or O	–	Usually	Very good to fair	Special
	D	–	Occasionally	Variable	Special
Garnet	N	All varieties	–	–	*Special
	E or H	Some demantoid	Commonly	Very good	*Special
Hematite	N	–	–	–	Normal
Iolite	N	–	–	–	Normal
Jade – Jadeite	E or W	–	Commonly	Fair	Special
	B and I	Green/purple/white	Commonly	Very good to good	Special
	D	–	Occasionally	Variable	Special
	B and W	–	Rarely	Poor	Special
Jade – Nephrite	D	–	Rarely	Unknown	Special
Kunzite	E or H	–	Commonly	Fair	Special
	R	–	Commonly	Fair	Special
Natural Gemstone	Enhancement Symbol	Description Used	Frequency Encountered	Stability	Care Requirements
Lapis lazuli	E or W	–	Commonly	Fair	Special
	D	–	Commonly	Variable	Special
Moonstone	N	–	–	–	Normal
Morganite	E or H	–	Commonly	Excellent	Normal
Opal	O	White/black	Rarely	Fair	Special
	I	–	Rarely	Good	Special
	O	Boulder	Usually	Good	Special
	D	Matrix	Commonly	Good	Special
	N	Fire opal	–	–	*Special
	I	Cat’s eye	Usually	Good	Special
	I/O/D	Hydrophane	Commonly	Good to fair	Special
Pearl – Natural	E or B	White	Usually	Very good	Special
	D	–	Rarely	Very good to good	Special
Pearl – Cultured	E or B	White	Usually	Excellent	Special
	D	Many colors	Usually	Variable	Special
	R	Black/gray	Occasionally	Very good	Special
Peridot	E or O	–	Rarely	Good to fair	Special
	F	–	Rarely	Good	Special
Ruby	E or H	–	Usually	Excellent	Normal
	Fh	–	Commonly	Excellent	Normal
	O	–	Occasionally	Good to fair	Special
	D	–	Rarely	Poor	Special
	R	–	Rarely	Unknown	Normal
	F	–	Commonly	Very good to fair	Special
	U	–	Rarely	Good	Special
Natural Gemstone	Enhancement Symbol	Description Used	Frequency Encountered	Stability	Care Requirements
Sapphire	E or H	–	Usually	Excellent	Normal
	U	–	Occasionally	Good to fair	Special
	O	–	Occasionally	Good to fair	Special
Sapphire – Fancy	E or H	–	Usually	Excellent	Normal
	R	Yellow/orange	Occasionally	Very poor	X-Special
	O	–	Occasionally	Good to fair	Special
	U	–	Occasionally	Good to fair	Special
Serpentine	D	Various colors	Commonly	Good to fair	Special
	E or W	–	Commonly	Very good to good	Special
Spinel	N	–	–	–	Normal
	O	–	Occasionally	Good to fair	Special
Sugelite	N	–	–	–	Normal
Sunstone	N	–	–	–	Normal
Tanzanite	E or H	–	Usually	Excellent	*Special
Topaz	R	Blue	Usually	Excellent	Normal
	R	Yellow/orange	Occasionally	Variable	Special
	R	Green	Occasionally	Poor	X-Special
	U	Green	Usually	Good	Special
	N	Brown	–	–	*Special
	E or H	Red/pink	Usually	Excellent	Normal
Natural Gemstone	Enhancement Symbol	Description Used	Frequency Encountered	Stability	Care Requirements
Tourmaline	N	Chrome green	–	–	Normal
	N	Cat’s Eye	–	–	Normal
	E or H	Yellow/orange	Rarely	Excellent	Normal
	R	Yellow/orange	Rarely	Very good	Normal
	E or H	Green/blue	Commonly	Excellent	Normal
	O	Any color	Occasionally	Good to fair	Special
	E or H	Pink/red/purple	Occasionally	Excellent	Normal
	R	Pink/red/purple	Commonly	Good	Normal
	D	Pink/red/purple	Occasionally	Fair to poor	Special
Turquoise	W	–	Commonly	Fair to poor	Special
	D	–	Rarely	Poor	X-Special
	I	–	Commonly	Good	Special
Zircon	N	Green/brown	–	–	*Special
	E or H	Blue/colorless	Always	Fair to poor	Special
	E or H	Yellow	Rarely	Good	Special
	E or H	Red	Commonly	Fair to poor	Special

Notes:

• The “N” symbol is used only for gemstones which we guarantee have not been enhanced.
• All jewelry (with or without stones) requires special care; some jewelry requires extra-special
  (X-Special) care.
• * Indicates a gemstone which generally requires special or extra-special care (although the need for care is not necessarily related to the enhancement).

ALEXANDRITE: A Buying guide

By Richard W. Hughes

Introduction
Alexandrite is the variety of chrysoberyl that displays a change-of-color from green to red. A distinct color change is the primary qualification for a chrysoberyl to be considered alexandrite. Although alexandrite is strongly trichroic, its color change has nothing to do with pleochroism. Instead, like all other color-change gems, it results in a near-equal transmission of the blue-green and red portions of the spectrum, coupled with strong absorption in the yellow. Thus its color is dependant on the spectral strength of the light source. Incandescent light is strongly tilted to the red end, thus causing alexandrite to appear reddish. Daylight, is more equally balanced. Since our eyes are most sensitive to green light, the balance is tipped to the green side. The strength of the color change is related to the difference in the areas of transmission, relative to the absorption in the yellow. The greater the difference, the stronger the color change.

This 1.89-ct. alexandrite, here shown in daylight (left) and incandescent light (right) comes from the famous Russian mines. Gem courtesy of Pala International. (Photo: Wimon Manorotkul; Gem: Pala International)

Color
For alexandrite, the quality of the color change is paramount. While the holy grail is a gem whose color changes like a traffic light from green to red, such a stone has yet to be found. In fine examples, the change is typically one from a slightly bluish green to a purplish red. The quality of color change is often referred to by dealers in a percentage basis, with 100% change being the ideal. Stones that display a change of 30% or less are of marginal interest and are arguably not even alexandrite. Significant brown or gray components in either of the twin colors will lower value dramatically.

Clarity
In terms of clarity, alexandrite is comparable to ruby, with clean faceted stones in sizes above one carat being rare and extremely rare in sizes above 2–3 carats. Negative crystals and parallel rutile silk are common inclusions.

Cut
In the market, alexandrites are found in a variety of shapes and cutting styles. Ovals are cushions are the most common, but rounds are also seen, as are other shapes, such as the emerald cut.

This 1.02-ct. alexandrite, here shown in daylight (left) and incandescent light (right) shows a nice color change. Gem courtesy of Pala International. (Photo: Wimon Manorotkul; Gem: Pala International)

Prices
Alexandrite is one of the world‘s most expensive gems, with prices similar to those fetched by fine ruby or emerald. But like all gem materials, low-quality (i.e., non-gem quality) pieces may be available for a few dollars per carat. Such stones are generally not clean enough to facet.

Stone Sizes
Facet-quality alexandrite rough is extremely rare. Thus even melee (less than 0.5 ct.) can sell for thousands of dollars per carat. Any fine faceted alexandrite above two carats should be considered quite large. Stones of quality above five carats are extremely rare. While Sri Lanka has produced some alexandrites above 10 carats, these generally do not display a good color change, moving from green to brown.

Name
The name “alexandrite” was coined by mineralogist Nordenskjöld, in honor of the former Russian czar, Alexander II, who came of age about the time the gem was discovered (supposedly on 23 April, 1830). An added factor was that the old Russian imperial colors of red and green are also the colors of alexandrite.

Sources
The original locality for alexandrite is Russia. Fine stones have also been found in Sri Lanka, Zimbabwe, Burma, Tanzania, Madagascar, India and Brazil. In 1987, an important new deposit at Hematita, Brazil was discovered. This mine produced for just a brief period, but a number of fine stones were found. In the mid-1990’s, Tanzania’s Tunduru region has also produced some outstanding specimens.

Imitations
While true synthetic alexandrites do exist, the vast majority of such stones are actually synthetic color-change sapphires colored by vanadium. Since synthetic color-change sapphires have been made from about 1909 onwards, it is entirely possible to have a piece that is nearly an antique. Indeed, many a traveler has returned from a third-world trip with what they think is natural alexandrite, only to later discover (or have their heirs discover) that what they have is a cheap synthetic sapphire worth but a few dollars per carat.

This 5.25-ct. alexandrite, here shown in daylight (left) and incandescent light (right) is an example of the finest of this gem variety. It comes from Tunduru, Tanzania, and was recently sold by Pala International. (Photo: John McLean; Gem: Pala International)

Properties of Alexandrite

	Alexandrite (a variety of chrysoberyl)
Composition	BeAl2O4
Hardness (Mohs)	8.5
Specific Gravity	3.74
Refractive Index	1.746–1.755 (0.009) Biaxial positive
Crystal System	Orthorhombic
Colors	Daylight: Green to blue-green Incandescent Light: Purple to purplish red Alexandrite is colored by the same Cr+3 ion that gives ruby and emerald their rich hues. Rarely, vanadium may also play a part
Pleochroism	Strongly trichroic: greenish, reddish and yellowish
Phenomena	Change of color, cat’s eye
Handling	No special care needed
Enhancements	Generally none; occasionally oiling, dying
Synthetic available?	Yes

RUBY: A buying guide

By Richard W. Hughes

Introduction
The term ruby is reserved for corundums of a red color, with other colors called sapphire. In Asia, pink corundums are also considered rubies. Outside of Asia, such gems are generally termed pink sapphires.

Color
For ruby, the intensity of the red color is the primary factor in determining value. The ideal stone displays an intense, rich crimson without being too light or too dark. Stones which are too dark and garnety in appearance, or too light in color, are less highly valued. The finest rubies display a color similar to that of a red traffic light.

Fine ruby specimens. The crystals are from, from left to right, Afghanistan, Vietnam and Tanzania, while the two faceted gems are from Mogok, Burma. (Photo: Harold & Erica Van Pelt; Gems: Pala International)

Lighting
Rubies generally look best viewed with incandescent light or daylight (particularly around midday). Avoid fluorescent tubes, which have virtually no output in the red end of the spectrum, and so cause ruby to appear grayish.

Clarity
In terms of clarity, ruby tends to be less clean than sapphire. Buyers should look for stones which are eye-clean, i.e., with no inclusions visible to the unaided eye. In the case of some rubies, extremely fine silk throughout the stone can actually enhance the value. Many rubies also display a strong red fluorescence to daylight, and this adds measurably to the beauty of this gem.
While a certain amount of silk is necessary to create the star effect in star ruby, too much silk desaturates the color, making it appear grayish. This is not desirable.

Cut
In the market, rubies are found in a variety of shapes and cutting styles. Ovals are cushions are the most common, but rounds are also seen, as are other shapes, such as the heart or emerald cut. Slight premiums are paid for round stones, while slight discounts apply for pears and marquises. Stones that are overly deep or shallow should generally be avoided.
Cabochon-cut rubies are also common. This cut is used for star stones, or those not clean enough to facet. The best cabochons are reasonably transparent, with nice smooth domes and good symmetry. Avoid stones with too much excess weight below the girdle, unless they are priced accordingly.

Prices
With the exception of imperial jadeite and certain rare colors of diamond, ruby is the world’s most expensive gem. But like all gem materials, low-quality (i.e., non-gem quality) pieces may be available for a few dollars per carat. Such stones are generally not clean enough to facet. The highest price per carat ever paid for a ruby was set on April 12, 2005 for an 8.01-ct. faceted stone that sold for $274,656 per carat ($2.2 million) at Christie’s New York. Previously the record for per-carat price was Alan Caplan’s Ruby (‘Mogok Ruby’), a 15.97-ct. faceted stone that sold at Sotheby’s New York, Oct., 1988 for $3,630,000 ($227,301/ct).

Stone Sizes
Large rubies of quality are far more rare than large sapphires of equal quality. Indeed, any untreated ruby of quality above two carats is a rare stone; untreated rubies of fine quality above five carats are world-class pieces.

Phenomena
Ruby may display asterism, the star effect. Fine star rubies display sharp six-rayed stars well-centered in the middle of the cabochon. All legs of the star should be intact and smooth. Just having a good star does not make a stone valuable. The best pieces have sharp stars against an intense crimson body color. Lesser stones may have sharp stars, but the body color is too light or grayish. On occasion, 12-rayed star sapphires are found. Inexpensive star rubies come mainly from India.

This 4.86-ct. star ruby from Pala International is one of the finest examples to come out of Mogok in years. (Photo: John McLean; Gem: Pala International)

Name
The name “ruby” is believed to be derived from the Latin ruber, a word for red. According to Oriental beliefs, ruby is the gem of the sun. It is also the birthstone of July.

Sources
The original locality for ruby was most likely Sri Lanka (Ceylon), but the classic source is the Mogok Stone Tract in upper Burma. Fine stones have also been found in Vietnam, along the Thai/Cambodian border, in Kenya, Tanzania, Afghanistan, Pakistan, Yunnan (China) and most recently, Madagascar. Low-quality rubies also come from India and North Carolina (USA).

Enhancements
Today, the vast majority of rubies are heat-treated to improve their appearance. The resulting stones are completely stable in color. Many rubies are also heated in the presence of a flux to heal their fractures, particularly those from Möng Hsu, Burma. In lower qualities and smaller sizes, heat treated stones sell for roughly the same as untreated stones of the same quality. However, for finer qualities, untreated stones fetch a premium that is sometimes 50% or more when compared with treated stones of similar quality. Other treatments, such as oiling, dying and surface diffusion are seen on occasion. As with all precious stones, it is a good practice to have major purchases tested by a reputable gem lab, such as the GIA or AGTA, to determine if a gem is enhanced.

Imitations
Synthetic rubies have been produced by the Verneuil process since the 1890s and cost just pennies per carat. Ruby has also been produced by the flux, hydrothermal, floating zone and Czochralski processes. Doublets consisting of natural sapphire crowns and synthetic ruby pavilions are fairly common, particularly in mining areas. Synthetics are also common at the mines, in both rough and cut forms.

Properties of Ruby

	Ruby (a variety of corundum)
Composition	Al2O3
Hardness (Mohs)	9
Specific Gravity	4.00
Refractive Index	1.762–1.770 (0.008) Uniaxial negative
Crystal System	Hexagonal (trigonal)
Colors	Various shades of red. Ruby is colored by the same Cr+3 ion that gives alexandrite and emerald their rich hues.
Pleochroism	Strongly dichroic: purplish red/orangy red
Phenomena	6 or 12-rayed star
Handling	No special care needed
Enhancements	Frequently heated; frequently flux-healed; occasionally oiling, dying, surface diffusion
Synthetic available?	Yes

TOPAZ: A BUYING GUIDE

By Richard W. Hughes

Introduction/Name
Topaz is the name for the mineral species that is number 8 on Mohs’ scale of hardness. There is some uncertainty regarding the name. Some say it comes from the Sanskrit word meaning “fire.” Others link it to the Red Sea Island of Topazios (Zabargad or St. John’s Island), where peridot has been found.
Ancient Egyptians thought the stone was colored by the mighty sun god Ra and was worn as an amulet against harm. During the Middle Ages, engraved topaz was used by clergy and royalty to promote goodwill. Topaz is the official gemstone of Texas and Utah and blue topaz is the gemstone of the 4th anniversary of marriage.
For the general public, topaz means a yellow gem, and much citrine and smoky quartz has been sold as “golden topaz” and “smoky topaz.” The terms “imperial” and “precious” topaz are often used to distinguish between true topaz and the quartz look-alikes.
The name “imperial topaz” is said to have originated in the 19th century in Russia, where the Ural Mountain mines were an important source. According to some sources, pink topaz from those mines was restricted to the family of the Czar. Today, the gem trade generally uses the term for pink, orange and red topaz, which comes mainly from Ouro Prêto, Brazil. Fine pink topaz also comes from the Katlang area of Pakistan.

Three different flavors of imperial topaz from Brazil. 4.8 cm. high. The most highly sought would be the pink gem at right. Gems: Pala International; Photo: Robert Weldon

Color
Topaz commonly occurs in colorless and brown colors, it is the rare golden, orange, pink, red and purple colors, which are often termed “precious” or “imperial” topaz, that are the mainstay of the fine gem market. While blue topaz is found in nature, most of the material is produced by a combination irradiation/heating treatment.
Yellow and brown topaz owe their color to color centers. The impurity chromium produces pink to red colors. A combination of color centers and chromium produces orange topaz. Blue topaz is colored by color centers.
Note that the color of some brown topaz may fade with time.

Lighting
Due to its orange to red-orange color, topaz generally looks best under incandescent light. In contrast, blue topaz looks best under daylight or fluorescent light. When buying any gem, it is always a good idea to examine it under a variety of light sources, to eliminate future surprises.

A gorgeous brown topaz crystals from the Mogok region of Burma. 4.8 cm. high. Crystal: Carl Larson collection; Photo: Jeff Scovil

Clarity
Topaz from most sources is reasonably clean. Thus eye-clean stones are both desirable and possible. The exception is with pink and red topaz, where only small stones are normally available. In those colors, a slightly higher degree of inclusions are tolerated.

Cut
Due to the shape of the rough (elongated prisms), topaz is generally cut as elongated stones, typically emerald cuts, elongated ovals, cushions and pears. To save weight, pears in particular are often cut with overly narrow shoulders. Due to the huge production, blue topaz is cut in virtually any shape and style one can imagine. Cabochon-cut topazes are rarely seen.
While topaz does have a perfect basal cleavage, it is not an easy cleavage, and so does not present too much difficulty to the cutter. Nevertheless, cutters will often try to ensure that no facet is parallel to the cleavage direction and jewelers try to mount valuable stones in settings that protect the stone.

Magnificent intergrown brown topaz crystals from the Mogok region of Burma. 8.5 cm. high. Crystal: William Larson collection; Photo: Jeff Scovil

Prices
The prices of topaz are, like any gem, dependent on quality. Still, a few generalizations can be made. Blue topaz, the most common variety seen in jewelry today, has been produced in such quantities that today it is generally available for $25/ct. at retail for ring sizes. Larger sizes may be slightly more. While natural blue topazes are known, the huge production of treated blue topaz has essentially dropped the price of the natural blue down to that of the treated stone.
Colorless topaz, from which blue topaz is produced (via irradiation and heat), is available in sizes up to 100 cts. and greater, and sells for less than $8/ct. Brown topaz fetches similar prices.
In contrast, precious topaz (a.k.a. ‘imperial’ topaz) in rich orange colors fetches prices in excess of $1000/ct. for large (10 ct. +) sizes. The most valuable topaz is a rich pink or red color, and can reach $3500/ct. at retail. These are rare in sizes above 5 cts.

Stone Sizes
Topaz sometimes occurs in enormous sizes, where clean gems of even 1000 cts. are known. Indeed, faceted stones of tens of thousands of carats have been produced from some monster crystals. However, cut stones of the prized “imperial” colors (orange, pink and red) are more rare. Fine pinks and reds above 5 cts. are scarce. Fine oranges above 20 cts. are also rare.

Three different examples of treated blue topaz. Gems: Pala International. Photo:Wimon Manorotkul

Sources
Gem topaz has been found at a number of localities around the world, including Brazil, Nigeria, Sri Lanka, Russia, Burma, Pakistan, USA and Mexico. The premier source is near Ouro Prêto in Brazil’s Minas Gerais state.

Enhancements
As previously mentioned, several varieties of topaz are typically enhanced. Most common is the combination irradiation/heat treatment that produces blue topaz. For this treatment, colorless topaz is irradiated, turning it brown. The stone is then heat treated, which turns it blue. While the brown color is generally unstable, fading with prolonged exposure to sunlight, the blue color is generally stable under normal wearing conditions.
There are three main flavors. The first, a “sky” blue, is produced by gamma rays (cobalt 60). Deeper “Swiss (a.k.a. ‘windex’) ” and “London” blues are produced by high-energy electrons (cyclotron) or nuclear radiation. In the latter case, the stones must be allowed to cool down to safe levels of radioactivity before being sold. This typically takes a few months to as much as two years.
Another treatment seen on occasion with topaz is bulk diffusion, where stones are heated for long periods surrounded by cobalt. This drives the cobalt into a thin layer at the surface, turning it green to blue. The layer is extremely thin.
Finally, some topaz is coated with metallic oxides, similar to the coatings on camera lenses. This produces various colors and rainbow-like reflections, but the coatings are easily scratched. The material has been marketed under the name “rainbow” topaz.

Imitations
Topaz has never been synthesized, but a number of imitations exist, including natural stones such as citrine and smoky quartz, and man-made imitations such as glass.

A magnificent 15.45-ct. imperial topaz from Brazil. Gem: Pala International; Photo: Wimon Manorotkul

Properties of Topaz

Composition	Topaz has the following composition:Al2(F,OH)2SiO4
Hardness (Mohs)	8
Cleavage	Perfect (but not that easy) basal cleavage
Specific Gravity	3.53 ± 0.04
Refractive Index	1.619–1.627 (±0.010)
Crystal System	Orthorhombic; usually occurs as vertically striated elongated prisms topped by domes
Colors	Orange, yellow, brown, blue, pink, colorless, rarely red
Pleochroism	Weak to moderate, dichroic
Dispersion	0.014
Phenomena	None
Handling	Ultrasonic: not safe; never clean topaz ultrasonically Steamer: not safe The best way to care for topaz is to clean it with warm, soapy water. Avoid exposure to heat, acids and rapid temperature changes. Strong heat may alter or destroy color
Enhancements	Various Most blue topaz is made by irradiation and then heat; this treatment is undetectable and extremely common Blue topaz irradiated with in nuclear reactors can emit dangerous levels of radiation; it must be allowed to cool down to safe levels before sale Some orangy topaz is heated to destroy the color centers, leaving behind the chromium-caused pink color
Synthetic available?	No