The article highlights the perils of buying colored gemstones in Brazil. People who visit Brazil buy colored gemstones with or without product knowledge. In all gem producing countries in the world, glass and synthetic corundum are the two most frequently encountered fakes. Even experts get taken for a ride because the fakes look so good. Sometimes we are distracted by other events when buying gemstones and become victims of ‘momentary autism’.
Read on to learn more……
(via The Canadian Gemmologist, Volume XII, Number 1, Spring 1991)
Some Fake Gems On The Brazilian Market And How To Identify Them
Joachim Karfunkel, Reinhard R Wenger, Wolney Lobato writes:
Abstract
After 15 years experience in the Brazilian gem market, the authors suggest a simple ‘micro-lab’ for the detection of imitations and falsifications. Descriptions of some of the most common fakes in cut stones, rough material, and specimens for collectors are given. Simple means for distinguishing them from genuine pieces are discussed.
Introduction
Brazil, a paradise on earth for gems, is also a territory with one of the highest incidences of gem and mineral falsifications. The story of imitations or fakes in gemology is probably as old as the first uses of minerals and similar materials for personal adornment. Webster (1983) writes: “It is, however, faience, a glazed siliceous ware made in Egypt as long ago as pre-dynastic times (before 4777 B.C) which is the more important as a beginning of imitation gemstones.”
We can define imitation as any substance used as a substitute for natural gem that fails to duplicate its composition, structure, and properties. Imitations aim to replace a gem with another cheaper material, which has a similar appearance, but different physical and chemical properties. Those imitations which have the purpose of misleading are called falsifications or fakes. To this group we could also add gems that have been treated to enhance their appearance, and supposed value, but which fade or change with time. Knowledge of these treatments should not be withheld from buyers. Further information on synthetics and gemstone enhancement can be found in Nassau, 1980, 1984.
The market for imitations in Brazil is huge, since most people there can’t afford to buy genuine gemstones. Similarly a metal other than gold is frequently used for settings. Imitations may be sold as genuine, and some regard the Brazilian market as a ‘cheating’ market. We want to emphasize that most of the Brazilian stone dealers are honest. Those few who want to mislead, however, sell their wares to everybody, including friends and even relatives! The problem is increased by lack of gemological education. The basic equipment is the human eye, sometimes aided with tweezers and a loupe. Most of those who possess a polariscope, dichroscope, refractometer, or microscope, usually don’t know how to use them. They sell the stones they bought believing truly that the stones are genuine.
The Micro-Lab
Many tourists, gem dealers and collectors prefer to buy in the interior of Brazil, rather than in the capitals like Belo Horizonte, Rio de Janeiro, Sao Paulo, Salvador, Fortaleza, or Porto Alegre. Obviously, it is very difficult to travel with a complete laboratory. We do not wish to imply that sophisticated equipment like refractometers, microscopes or spectroscopes is not important, but the tourist or collector often can’t afford such things, nor is it always possible to carry them in the field. Instead, we suggest a simple, cheap ‘micro-lab’ consisting of tweezers, loupe, polariscope, heavy liquid, and a hardness scale. Simple equipment can be effective when you understand how to use it.
Commercial polariscopes are usually expensive—why not build your own? Just buy a piece of Polaroid plastic and cut it into pieces about 2” square. Make a small stand (out of any kind of transparent, firm plastic), and glue the polaroid pieces on each side with the vibration directions perpendicular to each other. This polariscope may be used in the same manner as a conventional one. Place a light source (bulb, sunlight or torch) as near as possible to the polariscope. Hold the stone (rough or cut) between the filters with a hand or tweezers; rotate the stone, the polariscope or both, and observe the behavior (isotropic or anisotropic).
Heavy liquids are generally not cheap, but bromoform with a specific gravity of 2.83 at 15ºC can be acquired at relatively low cost. It should be emphasized that bromoform is a toxic substance, to be used only in a well ventilated area. Some practice is required to accurately estimate specific gravity, but the test is quick and even small stones (less than 0.5ct) may be measured accurately. The best method is by comparison: compare the rate of rise or fall of the unknown stone with that of a known one (indicator), possibly one of the specimens in the hardness scale. For example, the specific gravity of quartz is 2.65; beryl 2.7; pink tourmaline 2.05; fluorite 3.18; topaz 3.5; corundum 4.0.
You don’t need to buy a specimen for every number of hardness on the Moh’s scale. Small pieces of corundum (9), colorless topaz (8), quartz (7), feldspar (6), and apatite (5) will provide sufficient range of hardness and density. A piece of window glass, and a pocket knife are also practical. A piece of porcelain is useful to observe streak.
It may also be useful to have an ultraviolet lamp with short and long wave wavelength capabilities to detect adhesive on repaired or constructed specimens. Such a micro-lab is inexpensive and easy to carry.
Types of fakes
As the instances of fakes on the gem market are many, we can describe only a few and how they can be recognized. Imitations and fakes can be divided into three categories: cut stones, rough gem material and specimens for mineral collectors.
Fake faceted stones
Let’s look at the first group, cut and polished stones. You are probably not going to buy a Colombian emerald, an Indian spinel, or a Burma ruby in Brazil. The most common gems on the Brazilian market are topaz (blue and imperial), aquamarine, emerald, tourmaline, chrysoberyl (including cat’s eye and alexandrite), garnet (almandine and spessartine), amethyst, citrine, smoky and rose quartz, chrysoprase, agate, spodumene (variety kunzite), andalusite, sodalite, amazonite, hematite, etc. Less common are yellow beryl (heliodor), pink beryl (morganite), opal, green spodumene (hiddenite), fluorite, cordierite (iolite), kyanite, rhodochrosite, rhodonite, and apatite. More unusual gems like gahnite, petalite, scapolite, phenakite, amblygonite, brazilianite, titanite (sphene), diopside, euclase, etc and diamond will not be considered here.
On the gem market in Europe or the USA, you can find ‘well done’ imitations, sometimes difficult to detect without considerable gemological knowledge and equipment. In Brazil, however, cheap and readily available imitations such as glass, synthetic spinel, and synthetic corundum (both made by the Verneuil method) are common. Rarer are synthetic amethyst (hydrothermal), synthetic emerald (like Gilson and Chatham), synthetic corundum with a color change (Verneuil, alexandrite imitation) etc. Having a closer look at the Brazilian gems, we note that most of them are anisotropic except for garnet, which is isotropic, and agate and chrysoprase, which are cryptocrystalline varieties of quartz with a different behavior under the polariscope. The remaining opal, glass and synthetic spinel are opticall isotropic (with some anomalies). Knowing how to use the loupe and polariscope correctly, you can’t mistake these for one of the above listed gems. Almost all glasses on the Brazilian market have an S.G in the 2.52 region, and will float in bromoform. Most have an R.I around 1.52. An exception, dark violet in color, had S.G 3.18 and R.I 1.618; it sank slowly in bromoform. Don’t forget to use the loupe to look for bubbles and color distribution.
Most of the less common gems are also anisotropic, except opal (compare behavior in the literature) and fluorite. Many faceted violet fluorites were sold as amethyst in Belo Horizonte in 1986. This falsification is easily detected since fluorite is isotropic, and heavier than bromoform (3.18). Amethyst with an S.G of 2.65 floats, and is isotropic. It is much harder too, but hardness tests should not be carried out on a cut stone because they might cause damage.
Unfortunately synthetic emerald, synthetic corundum and synthetic alexandrite are not as easily distinguished from the genuine with the micro-lab, and require better equipment, including a microscope. Don’t buy ‘almost’ flawless stones with an excellent color without consulting a gemologist.
Characteristics of some glasses used as imitations
All the glasses were used to imitate gems of similar color.
Color: Violet; S.G = 2.52; R.I = 1.519; Optics = SR; 10x = Bubbles; Trace elements = Sr, Zr, Ba, La, Ce
Color: Honey yellow; S.G = 2.52; R.I = 1.518; Optics = SR; 10x = Bubbles; Trace elements = Pb, Sr, Ba, Zr
Color: Dark violet; S.G = 3.18; R.I = 1.618; Optics = SR; 10x = - ; Trace elements = Fe
Color: Medium blue; S.G = 2.52; R.I = 1.520; Optics = SR/ADR; 10x = Bubbles; Trace elements = Sr, Zr, Ba
Color: Dark blue; S.G = 2.52; R.I = 1.520; Optics = SR; 10x = - ; Trace elements = Sr, As, Sb
Color: Red yellow; S.G = 2.52; R.I = 1.518; Optics = SR; 10x = Bubbles; Trace elements = As, Se, Zr, Ba, Nd
Color: Green blue; S.G = 2.52; R.I = 1.518; Optics = SR; 10x = - ; Trace elements = Sr, Zr, Sn, Ba
Color: Emerald green; S.G = 2.52; R.I = 1.518; Optics = SR/ADR; 10x = Bubbles; Trace elements = Sr, Zr, Ba
Color: Light blue; S.G = 2.52; R.I = 1.519; Optics = SR; 10x = Bubbles; Trace elements = Sb, Zr, Sr, Ba
Note: The physical and optical properties were determined with an Eickorst refractometer, a Mettler scale, a GIA polariscope, a mineral light with short and long ultraviolet wavelengths, and Zeiss hand loupe 10x. The chemical analyses were kindly provided by Prof C Murtha and Prof R Murta (Nuclebras—Belo Horizonte) using x-ray energy spectrometry (detection limits for the above elements are 100ppm. All specimens are non-fluorescent in ultraviolet light except the red yellow glass, which weakly fluoresced a pale white in short wave UV)
Emeralds from the locality of Santa Terezinha, Goias, and those from Carnaiba/Socoto in Bahia usually have small black inclusions not seen in the synthetics (Gilson/Chatham). Only a few emeralds, some from the localities of Itabira and Nova Era, Minas Gerais, are ‘almost’ without inclusions. The prices are relatively high. So if you are offered such stones for US$200-300 per carat (one carat and larger), you can be sure that you have a synthetic in your hand.
Although corundum exists in Brazil (e.g ruby from Bahia and sapphire from Mato Grosso), the quality is very poor and usually not facetable. What generally appears on the market are Verneuil synthetic ruby and sapphire. Imitation alexandrites are frequently synthetic corundum with color change and not synthetic alexandrite. Synthetic stones of excellent quality, especially in old rings of 18 karat gold, are typically very poorly cut, and sometimes looked crooked. The old rule, ‘excellent gems have a very good cut, whereas low quality gems are poorly cut’ can be applied in this case. In larger stones, characteristic curved growth lines may be seen with the 10x loupe. Many of these stones, especially ruby, shows a very bright fluorescence with both long and short wave ultraviolet light.
Some fakes are so unexpected and simple that many buyers fail to recognize them because they don’t examine things carefully. For example, in the State of Ceara, northeast Brazil, a type of wax made from coconut (cera Carnauba) together with ink from a simple ballpoint pen is applied to white opal. The ink penetrates the opal and darkens it to simulate black opal. Examination with a 10x loupe will show concentration of the dark bluish ink along tiny crevices at the surface.
Falsifications of cat’s eye chrysoberyl may be made by irradiating asteriated quartz cabochons showing unusual strength of one of the rays. The color of the stone will turn brownish yellow, showing one strong ray only, thus imitating cat’s eye. A close look in different directions will reveal the asterism. If you are still in doubt, use the bromoform; chrysoberyl will sink whereas quartz will float.
Falsification of rough gem material
The second group, gem rough, is the easiest to detect, and there are only a few fakes on the market. Glass is commonly used to imitate tourmaline and aquamarine. In the case of tourmaline, green to bluish green glass has been fashioned into prismatic ‘crystals’ and even grooved with a saw to simulate the striations on a natural crystal. Upon magnification, these ‘striations’ appear to too regular. Other fake tourmalines are bicolored (e.g green and blue, green and red, or bright green and olive green) and often have inclusions (impurities). These are made from toy ‘marbles’, small glass spheres. Real tourmaline appears dark to almost black in the direction of the crystallographic axis (its optic axis); these will not. With the loupe it may be possible to detect bubbles in the glass and swirls of color. If there is still doubt, use the polariscope (not in the direction of the optic axis) or the bromoform. Bromoform will not distinguish between common glass and aquamarine, as both float, but tourmaline will sink. The polariscope will leave you without doubt.
Another fake on the market, already mentioned, is violet fluorite imitating amethyst. In 1986 thousands of grams of this material were sold in Belo Horizonte. Since fluorite is optically isotropic with a density of 3.18, you can detect it with either the polariscope or the bromoform. An examination with the hand loupe will show cleavage, usually in four direction(octahedral). Amethyst has no cleavage, and its hardness is 7 while fluorite’s is 4.
A different kind of falsification is exemplified by a parcel of golden beryl (heliodor), sold in the State of Paraiba in 1986. This ‘heliodor’ was nothing more than colorless beryl (goshenite) treated with a suspension of iron oxide or iron hydroxide to give it a yellowish color. A careful examination with the loupe shows that the coating is not homogenous, and you can see ‘windows’ of colorless beryl. Scratching a small piece with a knife will remove the coating.
Fake mineral specimens
The last and most difficult group to detect is mineral specimens for collectors—the variety is immense. We can divide this group into two categories: falsification strictly speaking, made out of other materials, and those using genuine minerals but glued in various ways.
For instance, pink crystal and watermelon crystal. Closer examination with the loupe is necessary to detect both falsifications The first specimen (pink crystal) consists of a sawn piece of lepidolite (a lithium mica) affixed to a matrix with powdered rubellite (red tourmaline) and cement. The striations are too regular, and with the loupe the granular structure of the coating material is obvious. Mica is also softer than tourmaline. The second example, sold in the city of Teofilo Otoni, Minas Gerais in 1973 for a very high price, simulates a watermelon tourmaline of excellent quality. The center is made from red glass. Green tourmaline, coarsely powdered, was mixed with common construction cement, and a green coating of this together with pieces of natural green tourmaline was applied around the red glass core. Here also, a close examination reveals the granular nature of the outer rim. Usually a huge tourmaline would appear very dark brown down the crystallographic c-axis (optic axis) which this fake does not. In this particular case, the polariscope will not separate glass from tourmaline, since tourmaline behaves isotropically in the direction of the optic axis. Well terminated crystals are of greater value to collectors than unterminated or broken ones. Faceted and polishing a broken end can make a crystal appear terminated. Examine suspicious crystals with the loupe. Polished areas generally look completely different from a natural crystal face. Tourmaline, aquamarine, ‘imperial topaz’, and quartz crystals are the most common minerals falsified in this manner.
The glued specimens of authentic minerals are even more difficult to detect. A specimen of scheelite and gold in matrix from the famous gold mine of Morro Velho, near the city of Belo Horizonte, was sold in 1987. A careful examination with loupe showed that the gold was glued onto the matrix. A piece of ‘canga’ (a conglomerate of naturally crushed rock particles, pebbles, and sand, with an iron oxide/hydroxide cement), with diamond and gold from the Diamantina District, Minas Gerais was seen, and both the diamond and the gold had been glued onto the specimen. Broken quartz crystals, also from the Diamantina region, are often seen glued back together. Since all three specimens do occur naturally, you have to examine the area surrounding the mineral (gold, diamond, or broken place) carefully using your loupe. A crystal or a piece of gold projecting from a crevice or a tiny cavity in the rock should arouse your suspicions.
Reaction of some adhesives to ultraviolet light
Adhesive: Araldite; Color: colorless to white; LW = white/yellowish/pink: very weak; SW = medium
Adhesive: Superbonde; Color: colorless; LW = -; SW = -
Adhesive: Silicone; Color: Colorless to white; LW = white to v.v.weak; SW = -
Adhesive: Durepox; Color: grey; LW = -; SW = -
Adhesive: Pattex Sekundenkleber (Germany); Color: colorless; LW = - ; SW = -
Adhesive: Pattex Extracola De contato; Color: white to yellowish; LW = white weak; SW = white medium
Adhesive: Bindulin Porzelankitt (Germany); Color: colorless to white; LW = violet weak; SW = violet medium
There are many adhesives on the Brazilian market, some of which are imported. Only a few of them fluoresce under ultraviolet light. More difficult to detect are those pieces like gold that are not glued, but rather forced into the matrix with a piece of wood. Examine the gold with the loupe to detect any ‘pushing marks’.
For example: Cut/polished agate with water: Magnification of the brownish/reddish point at the upper part reveals that the age was sawn, drilled with ultrasonic drill, then injected with water, and the hole closed with adhesive. Ten power magnification will show the tiny hole filled with glue, and short wave ultraviolet light shows a bright point of fluorescence.
Conclusions
Most fakes on the Brazilian gem market are easy to detect with basic gemological knowledge and the use of the suggested ‘micro-lab’. Since the number of such falsifications and their varieties is immense, we have discussed only a few typical examples. Remembering these, and imagining all possible variations, the buyer won’t be cheated or misled in most cases. For ‘almost’ flawless emerald, ruby, sapphire and alexandrite with good color and cut, it is better to consult a gemologist with more extensive equipment. Cheap imitations of these stones and the synthetic Verneuil stones are usually poorly cut.
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