How to differentiate synthetic and natural sapphire

    How to differentiate synthetic and natural sapphire

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    How to differentiate synthetic and natural sapphire

    by Ashutosh Roy

    A deep look shows signs of slow crystallization in case of natural sapphires. Sometimes some external elements in very small quantities are visible in original sapphire like most other gemstones.

    Sapphire – Natural versus Artificial

    Natural gemstones are taken out directly from the marvelous treasures of the mother earth. Then they are only washed, polished and cut into proper shapes. They are directly sold in the market keeping their originality intact without any intervention by human beings. They are never “processed” or “treated”.

    Sapphire Diamond Ring

    Likewise Synthetic gemstones are gifts of technology marvels and the very process indicates how to create a new form using all natural elements and solutions. The challenge in Synthetic gemstone is how closest it can hold the look and feel of the natural one.

    As the time changes real things are getting imitated as a rule of the human nature. May be, its for comfort, fashion or money-making urge of the greedy scientists engaged in the process. We all are habituated in the artificial cooling by air-conditioner. We may see, how an artificial shower pours down in a film. A test tube baby is also generated from a sterilized mother to see a laughing face, who would not otherwise have a natural baby for her thirsty heart. Similar is the case with a gemstone. Remember a synthetic gemstone has got the exact replication of the natural one in terms of physical and chemical properties. The look and feel and the optical qualities also remain the same. In short, glimpse and glitter remain the same.

    Now if we consider the case of Sapphire, it’s a birthstone of September; physically it belongs to the variety of mineral corundum. Now for the natural science students, all varieties of corundum excepting the red one are called Sapphire. The word comes from the Greek Sappherious. Astrologically, Sapphire seems to have magical power even for alleviating long-term misfortune and in particular, to cleanse the jumbled up thoughts to generate a wider vision, clarity and self-confidence. It was perhaps invented in the 19th century for crystal watch and today it’s a common phenomenon to use sapphire (natural or artificial) in high value watches because of its glittering appearances.

    Synthetic Sapphire

    Now lets have a closer look into the synthetic sapphire. It’s definitely very hard like the natural one, which is approximately 9 in Mohs Scale. Synthetic sapphire is made from the crystallization process of aluminum oxide at a very high temperature. The Verneuil technique is used for making synthetic sapphires. Researchers have tried by varying concentrations of Ni2+, Ni3+ and Cr3+ to generate a wide spectrum of colour.

    It’s very difficult to distinguish between the synthetic sapphire and the natural one. A deep look shows signs of slow crystallization in case of natural sapphires. Sometimes some external elements in very small quantities are visible in original sapphire like most other gemstones. The inclusions may be finger prints or like feathers or even may be like laces. If you don’t find any of them, try through magnification. Reddish tints, polysynthetic twinnings are very common to natural sapphires. The hexagonal patterned angular lines are found in Sapphire. “Negative Crystals”, the cavities, are found in natural Sapphires. Impurities of any sort are the most common phenomena in case of Natural Sapphire.

    If you compare the natural sapphire with that of Synthetic one, you will notice bubble like inclusions. Even feather like inclusions are also possible in case of natural ones. If they are placed under strong light, the shining becomes abnormal. But again its very difficult for the normal eyes to detect. Inclusions of various types can be tested by fiber-optic lighting. In case of synthetic one, the coloring agents give the gemstone its various artificial hues, which are never present in case of natural one. But remember the synthetic sapphire is not that disparaging like most other synthetic gemstones; sometimes even people ask for synthetic sapphires for their jewelries and watches.

    Remember the watch glass producers always prefer colorless synthetic sapphire. The Surface diffusion-treated corundum (SDTC), the revolutionary concept, has been accepted widely, for its coating functionality. Even being a processed sapphire, the SDTC has gained enormous popularity. “Cathodoluminescence Analyses” by Prof. K. Ramseyer at the University of Berne, Institute of Geological Sciences, Berne (Switzerland) have contributed to the design of fancy sapphires, which have again been accepted widely though being these fancy sapphires belong to the category of processed sapphire.

    Experts suggest, rub a gemstone in your palm and squeeze it between your fingers. The synthetic one will give you a waxy feel. Testing laboratories use different methodologies to identify the synthetics ones. Experienced eyes of gemologists can detect the synthetic one even by naked eyes and by its touch and feel.

    The ultraviolet radiation process is highly helpful for identification of Synthetic Sapphire. Sometimes the specific gravity comparison can also help to identify the natural one. The refractive index test is also useful for distinguishing between the natural and the synthetic one. The synthetic sapphire glows abnormally in the Special lighting effect. But again as an exception, even the natural orange sapphire is highly fluorescent. So don’t get confused! The microscopic view of synthetic sapphire shows the “Curved Striae”, which are colored curved bands in the sapphire. UV Fluorescence is used in many laboratories as a Gemological tool to identify the synthetic stones. Some uses the highly complicated testing method like Secondary Ion Mass Spectrometry (SIMS) for testing the natural sapphires. But the caution message is that heating is never a normal procedure to test a sapphire. Richard W. Hughes in “CORUNDUM IDENTIFICATION IN A NUTSHELL”, advises “complete Fe Spectrum of lines at 451.5, 460 & 470 nm. is proof of natural origin”. Perhaps this is the best full-proof solution.

    If you are a novice, try to go to a genuine gemstone mart, which is recognized or of immense repute. You may also try your personally known jewelers. Its always preferable to take help of reputed Testing & Research Laboratories like Gem and Jewelry Institute of Thailand (GIT), American Gem Trade Association (AGTA), Gemological Institute of America’s Gem Trade Lab. There are several grievance redressal forums today like “Jewelers Vigilance Committee” (Website: http://www.jvclegal.org) to address and take action on your complains.

    So if you really do believe in the myth that sapphire contaminated water even can save you from scorpion bite, try to be sanguine about the originality of the gemstone, else you may even risk your life!

    Amethyst Jewellery

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    Amethyst Jewellery

    by Binashaji

    The Amethyst bespeaks royalty and this stone can even overpower the personality of the person wearing it just by its royal appearance. The stone looks best when it is set in gold with diamonds, the combination of purple and diamonds is a classic. Of course, a single large Amethyst ring or a large pendant in dozens of tiny purple stones can catch the eye without the help of any other gems.

    Jewellery without gemstones is like Cake without Icing. It looks attractive but lacks the decorative, distinctive touch of colored gems. Adding gems in basic gold/silver or platinum Jewellery gives it dash of panache and elegance. The appearance and price of the ornament depends on the stone, setting and cut of the stone. It can range from formal, semi-formal, casual or just junk Jewellery. Enhancing the glitter of precious metals is the gorgeous stone – the Purple Amethyst. Purple is the color of Royalty and many stately families possess Amethyst ensembles, antiques – made from the highest quality Amethyst stones.

    The Amethyst bespeaks royalty and this stone can even overpower the personality of the person wearing it just by its royal appearance. The stone looks best when it is set in gold with diamonds, the combination of purple and diamonds is a classic. Of course, a single large Amethyst ring or a large pendant in dozens of tiny purple stones can catch the eye without the help of any other gems. Contemporary Jewellery designers have taken the purple of the Amethyst and combined it with Emeralds, Sapphires, Pearls, garnet and even Rubies to offer a palette of colors for fastidious customers. No excuse for not owning a piece of Amethyst Jewellery.

    Like most gems, color is an important deciding factor in grading Amethyst. A deep, natural purple color is more valuable than a lighter shade. Also like most gems, synthetic Amethyst is often passed as the real gem. The synthetic stones look so much like the natural stones that sometimes even Jewelers can be fooled. In fact, many jewelers buy rough synthetic at almost the same prices that they would pay for natural stones. The advantage is the same quantity of synthetic rough yields more stones than from the natural Ametyst rough. Technology advancements which made it possible to grow all kinds of quartz in laboratories under artificial conditions and these laboratory grown amethyst are also sold in the market as the natural stone. It is difficult for even the trained eye to differentiate the natural from the synthetic, although stores of repute do declare if an Amethyst is synthetic.

    The Amethyst is used not just for Jewellery but for Electronics and Crystal Therapy also. An Amethyst placed on the Crown Chakra (on the head) is believed to be beneficial in bringing harmony and peace to the mind. This stone has also been associated with celibacy and even today many Priests/Monks wear purple cloaks and even Amethyst rings to signify that they are not a part of the material world. Even the Buddhists believe in the power of purple and it is common to see Amethyst rosaries in Tibet. Healing, increasing psychic activity, lowering blood glucose and even inducing sobriety are among the many superstitions attributed to the Amethyst.

    Amethyst is a hard stone, measuring 7 on the Mohs scale. This makes it perfect for Jewellery. Being a hard stone, it can be fashioned and cut into almost any shape. Rings, Necklaces, Earrings or Bracelets – this vibrant stone available in many shades of violet make a passionate statement at every event. Whether you like light lilac or a deep royal purple, there is sure to be an Amethyst that you will want to own. But be sure to store it separately, it can cause other stones, which measure lower on the Mohs scale to be chipped. On the other hand, even the Amethyst can be scratched or chipped if a stone like a diamond – measuring higher on the Mohs scale, rubs against it.

    If you know an Aquarian, gift them an Amethyst, they will remember you for the rest of their life. It is also the anniversary gemstone for the 4th and 6th year of marriage. This passionate stone loses its color when heated, turning to a pale yellow from its natural violet shade. As with all Jewellery, protect your Amethyst from conditions that can cause it harm. Chemicals from hair sprays or perfumes, exposure to the sun and most important, if you need to get your Amethyst Jewellery polished or repaired, the stones have to be removed from their setting by the Jeweler before the metal is heated. It is easy to maintain the Amethyst. Just clean it with warm water and a bit of gentle soap and a soft brush to remove the grime. Or you can even use an Ultrasonic cleaner.

    While buying any Amethyst Jewellery, be sure to check the stones for a clear color with no cracks or other inclusions in the stone. Also be sure to buy from a reputed store that will be able to guide you to the right stone to match with your personality and budget. Of course if you just want something to liven up a bad day, purple junk Jewellery can do the trick. The Amethyst is a stone that suits both men and women and Amethyst rings on men look great.

    From Clerics to Fashionistas to Royalty, the lure of purple has enticed people from all backgrounds across centuries. Strong and passionate with a character of its own, the Amethyst is truly royal.

    Gemstone Testing tools

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    Gemstone Testing tools

    by Ms Nandita Ray

    It is tricky to test a gemstone. Some stones are soft, some are mounted while some can be coated, treated or easily scratched. One has to be very careful so as not to damage the stone in any way. With technology advancing rapidly, the tools used for testing are made to suit ones needs and pockets. Aiding the tools is a wide range of database, which lists the particular characteristics of gems.

    Tools Required to Test Gemstones

    There is an absolute and definite need to test gemstones, especially if they are expensive. Competition, economics, availability and demand have all worked towards the explosion of the gem market. The markets are flooded with gemstones of various hues, brand and breed. Therefore the need to test the authenticity of gemstones is imperative. Insurance too has a hand. They need the gem to be certified.

    In the past, it was pretty easy for a trained gemologist to distinguish a flawless gem from a flawed one. There were no synthetic gems during those days. Today however, one has to determine whether a gem is real or not. Trained eyes cannot always avoid error, particularly, if the gem has been manufactured in the laboratory. It becomes a challenging task. Earlier on a magnifying glass was good enough. Presently however, a host of instruments are used, especially if one wants to be absolutely certain of the gem, its history and pedigree.

    It is tricky to test a gemstone. Some stones are soft, some are mounted while some can be coated, treated or easily scratched. One has to be very careful so as not to damage the stone in any way. With technology advancing rapidly, the tools used for testing are made to suit ones needs and pockets. Aiding the tools is a wide range of database, which lists the particular characteristics of gems. This is valuable because the markets are deluged with zircons or the synthetic Moissanite, which are look alike diamonds and very difficult to differentiate from a real diamond.

    Loupe

    Loupe is actually a sophisticated magnifying glass. It magnifies the gemstone in detail. The internal flaws, surface blemishes, cracks and any other cover ups are easily seen. It is a powerful convex lens that produces a magnified image of the gemstone. The standard loupe that used is 10X, which magnifies the gem ten times its size. This standard is mandatory for testing gemstones in the USA.

    Binocular Microscope

    gemstone testing microscope image: www.ottofrei.com

    Binocular Microscope is equipped to spread light from the bottom and from the sides. Its function is similar to the loupe. Presence of the lights and its superior optical strength provides excellent clarity. It usually has 10X magnification power though 200X can be got. Most common ones are 10X to 40X. There are stages of adjusting the iris diaphragm. It also provides coarse to fine focusing.

    Refractometer

    Refractometer measures the refractive index of the gemstone. This is needed in order to find out its composition and physical properties. It measures the extent to which the light that passes through the gemstone from the air is bent. It helps identify the gem by comparing the refractive index thus got with the established values. It assesses the purity of the gem by comparing it to the value of a natural gemstone. It also determines the amount of solute that has been added to the gemstone by comparing the refractive index thus obtained with the standard curve that is established. This is done by putting a drop of a liquid with a high RI, on a glass disc which is based on the tip of the Refractometer. Natural or white light is passed through this. The RI is reflected in the magnified gauge.

    Dichroscope

    Dichroscope is used for the quick identification of gemstones. It can effortlessly separate gemstones based on dichroism, which is the property of a gemstone to show two contrasting colors when turned in two different directions, under a light. This is used to distinguish two physically similar looking gemstones. The dichroscope is used to view the dissimilar color tones of the dichroic piece. It can easily differentiate a Ruby from a Tourmaline, which is dichroic while a Ruby is pleochroic. Some gemstones that are dichroic are Sapphire, Topaz and Zircon, to name a few.

    Polariscope

    Polariscope is used to determine if a gemstone is natural or not. It can differentiate diamonds from Moissanite. It also detects strains in diamonds. It can differentiate between gems that have double or single refraction i.e. birefringence. Double refraction is the breaking up of a ray of light into two rays, the ordinary ray and the extraordinary ray, when it passes through some materials like calcite also called Iceland spar. This effect can take place in gems that are anisotropic in structure i.e. having properties that differ according to the direction of measurement. The polariscope helps to track and see the path the rays of light are taking through the stone that is being tested. By measuring the optic characteristics of transparent to translucent gem material, the refractive index is found. Double refractive is only a property of solids. For transparent materials, the graph of index, unlike the wave length, is curved with a few general characteristics. A gem is held between two polarized plates and the light transmitted through it is studied and based on the readings the identification is made.

    Some gemstones with double refraction are Quartz, Tourmaline, Ruby, Peridot, Sapphire, Zircon and Rulite to name a few. Diamonds are isotropic, meaning single refraction. Topaz, Mica and Perovskite have triple refraction.

    Ultra Violet Light source: – some gemstones start emitting a fluorescent glow after being exposed to short or long ultra violet radiation. Many gems can be easily recognized by the Fluorescent color and the locale. Some fluorescent minerals are Agrellite, Tugtupite, dolomite, Fluorite and Benotoite.

    Color Filter

    Color Filter is also called a ‘Chelsea Filter’ or ‘Emerald filter’. This instrument helps in separating natural, synthetic and imitation gem material. It helps in establishing whether similar looking stones exhibiting the same colors are natural or not. It comes handy while dealing with some green, red or blue stones, like blue Spinel and blue Topaz. It detects dyes in gemstones also.

    Spectroscope

    Spectroscope is also used to separate natural gems from synthetic gemstones. This is used in specialized gem testing laboratories. The differences in the chemical composition are revealed by the absorption spectrum of the light transmitted through the gemstone that is being tested. The instrument breaks up the light that is being transmitted from a gemstone into its spectral colors. This helps in testing the various wavelengths that are being taken in i.e. being absorbed by the gemstone. This indicates the type of elements that are present in the stone, which are absorbing the wavelengths. It allows the gemologist to see which color of light is being absorbed and thus identify the gemstone.

    Specific gravity Liquids

    Specific gravity Liquids – this is important for identifying a number of gemstones. A carat scale also called hydrostatic balance is used.

    X-Rays

    X-Rays are sometimes conducted to separate natural pearls from cultured pearls.

    Diamond Tester

    Diamond Tester is used for testing diamonds. The unit is switched on and the diamond that is to be tested is touched by a pointed tip. A light will come on to indicate if the stone is a genuine diamond or not. It uses thermal conductivity to differentiate diamond from its many stimulants. When the tip is touched to the diamond, the meter will show green if it is a real diamond if not then it will remain in the red zone. This instrument can be used to test the minutest diamond, as small as 0.02 carats. It can also separate colored stones from one another. By merely touching the thermo electric probe to the gemstone, the relative heat conductivity of the material is exhibited on the dial.

    These are the basic instruments. There are improved and sophisticated versions of these instruments available in the markets.

    Chelsea Filter

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    Chelsea Filter

    by Ritika Changrani

    Also known as Emerald filter, Chelsea filter is used to identify natural, synthetic and imitated gemstones. Developed by the British Gemmologists Anderson and Payne, this filter was initially developed only for the separation of natural emerald from green beryl. Now it is being used to identify various gemstones.

    Chelsea Filter – Gemstone Testing Tool

    chelsea filter

    Chelsea filters are designed to absorb all lights except red and yellow green which are transmitted through the filter. This causes different gemstones to exhibit different colors when observed through the Chelsea filter. Emeralds, when seen through the filter, appear red or pink in colour, while ruby appears brilliant red. Synthetic blue spinals appear yellowish orange or pink while the gems which are imitations appear green or greenish grey. Cobalt glass imitations of sapphire appear deep red.

    How to use a Chelsea Filter

    Hold the Chelsea filter close to the eye – may be at a distance of an inch or two from your eye. Provide strong light to the gemstone by lighting with a torch or bulb. Hold the torch or bulb such that the light falls directly down on the stone. When viewed from the filter, the stone may appear to change its colour. Never hold the Chelsea filter close to the stone since it may produce wrong results.

    How does a Chelsea Filter Work?

    Chelsea Filter works based on the characteristics of the gemstone. The Chelsea filter detects the presence of chromium and cobalt in the gemstone. Chromium, if present in the gemstone, produces red and green colour as in ruby and emerald, and the presence of cobalt gives a blue colour. It is the amount of chromium or cobalt present which gives a dark or light colour.

    When white light is passed through a gemstone, it absorbs colours of some wavelength and lets other colours free. The other colours which are not absorbed by the Chelsea filter mix up and give the colour appearance to the eyes. Depending on the appearance of the colour when viewed through the Chelsea filter, it is easy to detect the type of gemstone it is. For example, when white light is passed through the Emerald, emerald absorbs all the yellow-green wavelengths. Chelsea colour filter can filter all the colours except yellow-green and deep red wavelengths. Since yellow-green wavelength is already absorbed, only the red colour passes through the Chelsea filter.

    One has to make sure that there is enough light on the stone, else the reaction may not be visible to the eye.

    Gemstones identified by Chelsea Filter

    Red Stones

    Red stones that contain chromium are Burma ruby, synthetic ruby and red spinel. Ruby and spinel when viewed through the Chelsea filter appear red. Demantoid Garnet when examined through the Chelsea filter in presence of light appears pinkish. Though Thai ruby and pyrope garnet contain chromium, there is no colour change observed due to the presence of iron in those stones, which prevents colour change. Red stones like garnets and paste do not contain chromium and hence there is no colour change. When viewed through the Chelsea filter, they appear dark red or black in colour.

    Therefore when you are examining a group of red stones, you can easily separate different kinds of gemstones. Those which impart brilliant red are synthetic rubies. Stones which glow slightly red are natural rubies and spinals. Thai and Demantoid garnet may turn pinkish or slightly red. The stones which remain dark red or black are paste and other garnets.

    Green Stones

    Beryl is a green coloured stone which is coloured by chromium. The different types of beryl are emerald and aquamarine. Natural emeralds have a smaller amount of chromium, while synthetic emeralds have larger amount. Hence the change in natural emeralds is to dull or a little bright red. Synthetic emeralds change their colour to bright red. Some synthetic emeralds produce a dull red colour due to the presence of iron. Some natural emeralds like South African and Indian emeralds do not produce any red glow when viewed through the Chelsea filter. Chelsea filter can just give an idea that the gemstone may or may not be an emerald but the test is not a proof of detecting an emerald.

    Some stones can be confused with the emerald. They are Demantoid garnet, green garnets or savolite and tourmaline. All these stones when tested using the Chelsea filter, appear to glow red and are often mistaken to be emeralds.

    Green gemstones can be distinguished from each other by some of their characteristics. Emeralds produce an oily luster when seen through a Chelsea filter. Green garnets appear brighter than emeralds. Green zircon appears pinkish in colour and exhibits double refraction. Tourmaline is also a stone which exhibits double refraction. When green zircon and tourmaline are viewed through a 10X lens, the back faces of the stones appear to be doubled. Aquamarine has iron content due to which the colour produced is dull. The colour change in aquamarine is from blue-green to muddy grey-green. Green garnet, green zircon and chalcedony show very little colour change and appear pink or red. Pastes, green sapphire and peridot appear remain dark-green. Alexandrite appears red when seen through the Chelsea filter.

    Blue stones

    Blue stones contain cobalt which can be detected by the Chelsea filter. The colour change of blue stones when viewed though the Chelsea filter is red in highly doped stones and orange brown or green in light blue stones. The colour change to red when viewed though the Chelsea filter is an indication that the gem stone is synthetic. Sapphires show no colour change and remain dark blue or black.

    How to take Care of a Chelsea filter

    • It is recommended not to touch the Chelsea filter as it may leave marks on the glass. A soft dry cloth must be used to remove the dust.
    • Never put the Chelsea filter in water or any liquid.
    • The Chelsea filter must not be allowed to get heated either in direct sunlight or on a radiator.
    • When not in use, the Chelsea filter must be kept closed.

    Chelsea filter is an important tool in the field of gemology which can be used to test various stones. Although, the test is not cent percent reliable since the composition of every gemstone is not the same even in the similar type of stones, it is used by a number of gem testers for testing the gemstones.

    More Info: Gem Testing Tools

    Spinel Identification

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    Spinel Identification

    by Erum Qureshi

    A gemstone purported to be a spinel undergoes stringent tests in the lab for authenticity and grades (i.e. quality). It has distinctive characteristics and traits that a gemologist can easily identify.

    spinel courtesy: Orbital Joe

    image courtesy: Orbital Joe
    The mineral spinel produces a lovely suite of gemstones which are overshadowed by the more opulent ruby and sapphire. After ruby, spinel is perhaps the most beautiful of all red gems. Its colors vary from the lightest pink to a deep ‘garnet’ red. A beautiful ‘flame’ orange, magnificent cobalt-blue and a subdued blue-green are also some color varieties of this mineral.
    The derivation of the name’ spinel’ is obscure; its origins lie probably in the Latin ‘spina’, meaning thorn. It may also be derived from the Greek word, meaning spark, so christened because of its fiery red color.

    Species

    Spinel is a gem species by itself and is an aluminate of magnesium. Other members of the spinel group are Gahnospinel, (dark green), Gahnite (blue, dark blue), Hercynite (dark to black), Ceylonite or pleonaste (dark colors), Picotite (dark green to black) and Galaxite (dark red to black in color).

    Hardness

    Spinel is comparatively hard, (rating 8 on the Mohs scale of hardness). It shows an uneven cleavage and a conchoidal fracture and has a brittle nature.

    Determination of Specific Gravity

    Each gemstone has its own specific gravity or ratio of its weight to the same volume of water.

    The specific gravity is measured by immersing the gem (spinel in this case) in a series of heavy liquids, (usually a set of three liquids of varying densities). The gem will float in a liquid of higher density, sink in a liquid of lower density and remain suspended in a liquid of the same density. Although the density/specific gravity of spinel varies from 3.58 to 3.98, gem grade spinel range from 3.58 to 3.61. Pale pink stones have much lower values.

    Refractive Index

    Light rays leaving one medium and entering another obliquely seem to bend a little at the place of contact. This is called refraction of light. Refractive indices for spinel are measured by placing the stone face down in a Refractometer and a reading is taken. The mineral spinel has an RI in the range of 1.712 to 1.80. However gem quality spinel will have a fairly consistent RI, steady at 1.718. In red stones rich in chromium, it may rise up to 1.74. Ceylonites have values from 1.77 to 1.80.

    Absorption Spectra

    The absorption spectrum of red and pink spinel is typical of stones, which owe their color to chromium. In a spectroscope, which is an instrument used to determine the wavelength of the absorbed white light when it is passed through the gemstone, the spectrum is characterized by a broad absorption in the yellow-green, and absorption in the violet. There are no lines in the blue window and faint ones in the red. The wavelength is measured in nanometers (symbol nm) or angstrom symbol ?. The absorption spectra of red spinel (in nanometers): 685, 684, 675, 665, 656, 650, 642, 632, 595-490, 465, 455. (Strong absorption lines are in bold letters; weak ones are in parenthesis.)

    Fluorescence

    The luminescence of spinel shows considerable variation. Natural red and pink spinel show a strong red glow under long-wave UV light, and weaker under short-wave fluorescence. Dark blue spinel are completely inert under any radiation.

    Microscopic Examination

    As with any other gemstone, the final call on its identification and indeed its authenticity depends heavily on its microscopic examination and the ability of the gemologist to successfully differentiate between natural inclusions and those commonly associated with synthetics. Common natural spinel inclusions include ‘spangles’ which are included crystals with surrounding iridescent stress fractures. Other common inclusions are octahedral crystals or cavities filled with calcite or dolomite. Synthetic spinel have inclusions which include gas bubbles with torpedo shapes and long parallel hose-like tubes. Most (but not all) synthetic red spinel display obvious curved growth lines which appear as broad swathes of color.