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Does the refractive index change when a natural gemstone is treated to become a different color, or “man made”?Reply
The discovery of topaz may be one of the most legendary cases of mistaken identity. When Brazilian authorities reported the finding of a 1,680 carat diamond in Brazil, it was believed to be the biggest diamond ever. In fact, it was even set in the crown of the Portuguese king as a salute to his status and wealth.
When it was revealed to be a colorless topaz, it somewhat decreased in monetary worth, nevertheless, the power of the topaz has never diminished. It is highly valued today for its ability to impart strength and protection to its wearer and in its own right as beautiful and much sought after gemstone.
Although today we know that the topaz is not a diamond, it still remains a highly sought-after gem. It is the most durable silicate gem and available in a wide variety of colors. Although topaz is most commonly associated with a golden brown color, the rarest come in blues, pinks, reds and golden oranges. So rare are some of these colors, in fact, that most topazes must be enhanced in order to achieve these colors.
This article will discuss the following:
The Brazilians weren’t the only ones that incorrectly identified the topaz. The word “topaz” comes from the Greek name “topazios.” Topazios is the name of a Greek Island in the Red Sea, which is rich in minerals. Unfortunately, Topaz is not one of them. When the Greeks discovered what they thought to be vast amounts of topaz proved to be peridots. Apparently, explorers had mistaken the green hues of the stone with the amber color of the topaz. Although the topaz was not found in Topazios, it is found in pegmatite.
Pegmatite is a coarsely grained igneous rock composed almost entirely of crystals and minerals. The composition of pegmatite is rather simple. Most are made up of no more than K-feldspar, and quartz, with a few minerals thrown in that, define them from one another. However, there are more complex pegmatites which contain rarer minerals. Topaz is one of these minerals.
Topaz is a silicate mineral, which belongs to the orthosilicate group. The word orthosilicate indicates that the topaz has isolated silica tetrahedra which are separated from one another in a three- dimensional body. In addition to the simple pegmatite composition, the topaz contains the volatile components F- and OH-. The chemical composition for topaz is Al2SiO4 (F, OH)2.
Topaz is considered volatile because it must be formed in an environment which is already conducive to topaz growth. These environments occur when the granitic magma is almost completely crystallized and the compatible and volatile residual fluids in the magma create favorable conditions for the topaz to form.
These fluids may include fluorite, cassiterite, beryl, apatite, tourmaline, and lithium. Topaz may also form in rhyolite (the volcanic equivalent of granite), and in greisen, (granitic rock with intrusions of magmatic fluids. Quartz, feldspar, and mica are other minerals that are typically present in topaz bearing rocks.
Although topaz is most commonly found in an amber color, a variety of impurities can leak in as the topaz forms creating a variety of hues. Topaz can be found in wine red, pale gray, reddish-orange, pale green, or pink (rare). When chromium replaces the aluminum in topaz the red and pink varieties are produced. However, although the number of colors of the natural topaz is vast, the colors themselves tend to look washed out, which is why most of the topaz you will find on the market is heat-treated or irradiated.
Topaz is rarely ever created in labs for one simple reason, it’s not a valuable enough gem. Companies would rather spend money and resources on Diamonds and other precious gems that are more sought after.
That said, it’s common for Topaz to be treated in labs to enhance their chemical properties.
There are many forms of treatment which can be applied to stones. Colorless topaz is often irradiated, heated and covered with metal oxides to enhance and impart color to the stone.
When you look at light blue topaz, it may be difficult to believe that topaz begins life as nearly colorless. The color enhancement in blue topaz is due to a process called irradiation.
There are two types of irradiation used to color blue topaz. Neutron bombardment in a nuclear reactor causes the greenish or grayish "London Blue" topaz. An electron bombardment in a linear accelerator produces the aqua or "Sky Blue" and combinations of both leads to the highly saturated "Electric" and "Swiss" blues. If neutron bombardment is used, it may take up to a year to ensure the stone is "cool" enough to wear.
Mystic topaz is another popular treated topaz. In mystic topaz, the topaz is covered through a CVD (chemical vapor deposition) process with shades of red, teal, and an array of multicolors to create an iridescent stone. Although topaz treated with this process can be very beautiful, the process is not permanent, and the stones must be handled with extreme care to avoid scratching or abrasions.
Natural pink and purple topaz is extremely rare, but it can be produced in a laboratory through heat treatment. The process begins with a colorless topaz, which is heated and coated with a layer of metallic oxide to impart the vibrant pink hue that is often associated with the “Imperial” or “Precious” topaz.
The value of a topaz is determined largely by its color. The highest values go to the pink and red stones, and then to the orange and yellow. The “Imperial” topaz or “precious” topaz is an intense red and orange color; the yellow and brownish hues of topaz are less desirable, and more commonly found in nature.
While topaz of intense color is not likely to be found in nature, topaz can be treated to produce the vivid pinks and brilliant deep blues that are the most desirable. Naturally occurring topaz is colorless or pale. It needs to be treated in a lab to achieve the striking blues, bright greens and pinks that bring it to its full potential.
Those who buy untreated gemstones are usually investors. They know that untreated gems can retain their value over time. Whether or not they chose to buy them depends largely on budget.
Since the topaz is a common gem type, it is not likely to appreciate greatly in value, and may not be the more sensible choice for most consumers, investors or otherwise. In addition, buyers of natural topaz may end up sacrificing size for quality, as large natural high-quality stones can run very high in price.
If the visual appeal is more important, the treated topaz is the more sensible buy. If clarity, cut and color are your main concerns, the lab -treated topaz will give you a bigger selection to choose from, since most of the gemstones available today cannot be found otherwise.
The Moh’s scale of hardness is a scale which goes from 1 to 10 that rates minerals on their ability to scratch one another. The diamond rates a ten. It is the hardest mineral known to man. Only another diamond can scratch a diamond, a diamond cannot be scratched by anything other than a diamond.
Although not the highest rated mineral in terms of hardness, the topaz is the hardest silicate mineral. On the Moh’s hardness scale it scores an 8 third hardest mineral behind diamond and corundum, making it a very durable and practical stone.
Despite its high rating on the Moh’s scale, topaz may need to be treated a little more delicately than other minerals. When allowed to grow unrestricted, the topaz forms orthohydrogen crystals with striations parallel to the crystal’s the crystal’s long axis. This cleavage means that the topaz is more fragile than the hardness rating 8 would imply and can break on a plane when struck with sufficient force.
The hardness and durability of the lab treated topaz scores an 8 as well. Nothing is done in the treatment of the topaz to alter or fortify it. The cleavage issue is addressed in the cutting of the topaz. A bezel cut topaz will reinforce the planes and make the stone less likely to shatter and is the preferred cut for most consumers.
The GIA grading system for gemstones separates color into three categories: hue, tone, and saturation. The most common hues are red, orange, yellow, green, purple, and violet. Tone refers to the lightness or darkness of the stone and ranges from 0 (colorless) to 10 (black). Saturation is determined by the intensity of the stone’s color. Saturation ratings go from 1 (grayish brown) to 10 (vivid).
The most highly rated topaz is the Imperial Topaz. It features an orange-red hue (oR), a medium tone (5) and a strong saturation. Thus, the color grade would be noted as oR/5/5.
The highest rated blue topaz is greenish blue with medium to strong saturation. It receives a color grade of (vslgB/gB/5/5).
Brown and sherry colored topaz is found commonly and is often of relatively low value, although garnet like inclusions greatly increases its worth. Mexico is known for its production of fine brown topaz, much of which displays tones of deep red in one direction.
Although these colors are widely sought after, they are not widely found on the market. The topaz found in the earth is colorless or milky and requires heat treatment or irradiated in order to achieve the most desirable hues, tones, and levels of saturation.
While all treated topaz is designed to satisfy top color standards, a natural topaz has little chance of doing the same. It is unlikely to find a natural topaz which compares to the beauty and brilliance of treated topaz.
Clarity is the assessment of the internal and surface imperfections or inclusions in a stone. Clarity is very important in choosing a diamond and is one of the 4Cs that are commonly used to determine a diamond’s worth. A diamond’s clarity is graded strictly by the GIA, or Gemologists Institute of America. GIA diamond grading goes from IF (flawless, the most valuable) to I (included, the least valuable).
However, when it comes to gems, the standards for clarity are different. Some of the beautiful and unusual colors and features in gemstones are the results of impurities, so when it comes to determining clarity in gemstones, imperfections are tolerated as long as they don’t interfere with the stone’s beauty.
Although there is no international standard for grading gems, the GIA has come up with a system that separates gems into three categories: Types 1, 2, and 3.
According to this system, topaz is a Type 1 gem which means it is virtually inclusion free on the market. Since the inclusions in a topaz can only be seen under 10X magnification, it is considered “loupe clean” which means the inclusions in it cannot be detected by the human eye.
Because of the high clarity found in a topaz, no extra treatment needs to be done to enhance it. The clarity of the heat- treated topaz is just as high in clarity and unobstructed as the natural, and you can expect both to be equally eye-catching and radiant.
When we use the term “bling” we are not usually thinking of it as anything other than a slang word used to describe jewelry that is very noticeable and expensive looking, but there is actually be more to it than what meets the eye.
The "bling" of a stone is very important in establishing the stone's value. A stone’s bling factor depends on two things: its ability to reflect white light (sparkle) and its ability to break white light into colors (dispersion). These play a large role in determining the worth of a topaz.
As a general rule, lighter color gemstone will display more fire than darker colored ones Topaz that shows the most fire are the "Imperial cut" which tend to be pink or orange in color. Dark blues and browns and display less fire.
However, color is not the only thing that effects the topaz dispersal, cut is important as well. Topaz is a versatile stone and can be cut into a variety of shapes to increase its level of dispersion.
Strongly colored topaz is usually scissor cut to focus attention on their color whereas weakly colored stones are more likely to be brilliantly cut to enhance their fire. When a topaz has irregular infractions, it may be cabochon cut to conceal flaws.
The topaz is a transparent or translucent stone which is highly prized for its luster and brilliance. The refraction index of a stone is used to rate a stone’s brilliance, the dispersal chart is used to determine the fire of a stone. The refractive index of a topaz is 1.63 to 1.64 and is known for its relative sparkle, the dispersion of a topaz is 0.014.
Ideally, we would love nothing better than to sport and all-natural Imperial topaz on our fingers, but the chance of that happening are few and far between.
However, that does not mean you can’t find a real topaz just as impressive and beautiful. Lab treated topaz is real topaz enhanced to recreate the legendary beauty of the natural topaz at a reasonable price and in a convenient location.
A natural topaz may be something worth investing in, but if your desire for topaz is more about visual appeal than monetary appreciation, the lab-treated topaz is the more practical alternative.
What do you think? Would you rather have a gorgeous lab treated topaz on a ring, or a natural topaz sitting in a drawer? Would you consider buying the lab-treated topaz?
Does the refractive index change when a natural gemstone is treated to become a different color, or “man made”?Reply
I am looking for matching 7mm imperial trillions, preferably topaz toward the blue/green lab grown, matching 7mm trillions inTanzanite might work . As a last choice maybe pink, absolute bottom would be natural Peridot.Reply