Identifying a gemstone or gem is a difficult task.

The wide variety of gems (precious stones) available in nature represent a divine gift to us. Its colors and crystalline structures have enchanted us for thousands of years.

And we, jewelry professionals, give them shapes and facets that enhance their brightness and value, when applied in a creative way, in a jewel.

Despite being a source of enchantment and fascination, real gemstones are difficult to identify, as imitation productions and synthetic options grow rapidly, causing confusion between what is true and false.

Today, the big problem is how to identify a precious stone or gem from a synthetic stone.

Probably the first precious stones were found in riverbeds.

With the evolution of civilizations and the great interest in them, specific techniques were developed to search for these gems in nature.

The extraction and commercialization of precious stones has been done for thousands of years.

Over the centuries, the term precious stone acquired the meaning of a natural mineral desirable for its beauty, valuable for its rarity and very durable for its resistance.

This process caused these natural gems to have their prices soaring. The rarer, the more expensive.

With this great appreciation and rarity, imitations and synthetic gems emerged.

Today, it is difficult to identify natural stones, as synthetic and imitations have been perfected in their production processes.

Soon after the first forgeries, gemology emerged – a science derived from crystallography that defines concrete parameters for the evaluation and classification of gemstones.

Gemologists use equipment and tools within these standards and follow international evaluation routines.

In this way, when you intend to buy a very valuable gem, the best way is to hire the services of a gemologist. 

Precious and Semiprecious Stones

The distinction between precious and semi-precious stones has never had scientific validity. Today all stones, both minerals and rocks, appreciated for their beauty, durability and rarity, must be called gems.

To understand how this modification took place, it is necessary to know a little about the history of the gems. The denomination precious stone was used only for diamond, emerald, ruby ​​and sapphire, known as cardinal gems, as these had ecclesiastical, devotional or ceremonial use; the other gems were called semiprecious.

However, this term is debatable and confusing, and devalues ​​gems such as opal, aquamarine, chrysoberyl, amethyst or alexandrite, among other Brazilian stones of great beauty. Thus, the distinction between precious and semi-precious stones should be avoided by using the term gem.

The main Brazilian Gemstones

Among the various Brazilian gemstones, tourmalines and various types of beryls stand out.

1. Beryls

The mineral beryl is a silicate of beryllium and aluminum that has a prismatic or columnar habit, with a hexagonal base, hardness of 7,5-8, specific gravity of 2,63-2,80. It has a vitreous luster and can be transparent or translucent, with weak cleavage.

Pure beryl is colorless but can be tinted by impurities; with the following colors: green beryl is called emerald (presence of ferric iron or chromium), blue beryl is aquamarine (due to chromium and vanadium), pink beryl (due to manganese and iron) is morganite, bright and clear yellow or greenish-yellow beryl (due to manganese, iron and titanium) is called heliodor, colorless beryl is goshenite.

The rare red beryl is known as red emerald or bixbite.

Rough emerald in the rock
Rough emerald in the rock
Beryl cut varieties, from left to right, bixbite, morganite, heliodor, aquamarine and emerald
Beryl cut varieties, from left to right, bixbite, morganite, heliodor, aquamarine and emerald

2. Tourmalines

Tourmaline group minerals are boron and aluminum silicates, with variable composition due to the substitutions that may occur in their structure. The elements that commonly participate in the substitutions are Fe, Mg, Na, Ca and Li. Tourmalines exhibit prismatic habit, ranging from long and slender crystals to thick columnar, with triangular basal section, hardness 7-7,5, specific weight between 2.9-3.2.

They are transparent to opaque, with a vitreous luster and display well-marked vertical striations that help to identify them.

Tourmalines are divided according to their color: dravita: brown; schorlite: black; elbaite: green; rubellite: pink; indicolite: dark blue; acroite: colorless, among others.

Bicolor varieties occur, the best known is the watermelon tourmaline, whose colors are pink inside the crystal and green on the outside. There is a very valuable type of tourmaline, the Paraíba tourmaline, of an intense light blue (known in the trade as neon blue, fluorescent blue or electric blue).

Tourmaline varieties - rubellite (pink), elbaite (green), Paraiba tourmaline (blue)
Tourmaline varieties – rubellite (pink), elbaite (green), Paraiba tourmaline (blue)

synthetic gems

Synthetic gems are those produced in the laboratory and have a counterpart in nature. These materials have the same chemical composition, crystalline structure, physical and optical properties of their natural equivalents.

The Gemological Institute of America (GIA – Instituto Gemológico da América), the largest and most respected institution for the research and study of gems, describes on its website that a synthetic gem is one produced in a laboratory, but which shares all the chemical, optical and and physics of a corresponding natural mineral, although in some cases, for example in synthetic turquoise and synthetic opal, additional compounds may be present.

artificial gems

Artificial gems are those produced in the laboratory and that do not have an equivalent in nature, such as cubic zirconia, used as an imitation of diamond (JUCHEM; BRUM, 2010).

Shah (2012) differs between artificial and synthetic gems, stating that artificial gems are gems that have no counterparts among natural stones, they are made entirely by man; synthetic stones are crystallized or recrystallized materials, whose manufacturing method is totally or partially caused by man, but which have the same physical and chemical composition and optical properties of natural stones.

The Gemological Institute of America (GIA - Instituto Gemológico da América) cites as main artificial gems cubic zirconia (zirconium oxide), yttrium aluminum garnet (YAG), gallium gadolinium garnet (GGG), fabulite (titanate of strontium), and moissanite (silicon carbide), almost all of these synthetic gems simulate diamond.

Artificial gemstones (A) Cubic zirconia; (B) GGG; (C) YAG; (D) YAG before lapping
Artificial gemstones (A) Cubic zirconia; (B) GGG; (C) YAG; (D) YAG before lapping

gem imitation

Imitations are simulacra of natural gemstones, imitating their color and appearance. Imitations are different from synthetic gemstones and can be distinguished from natural and synthetic gems by their completely different physical properties and chemical composition. Imitations are mainly made of glass, paste or rhinestones, earthenware, porcelain and plastics, they are molded and not polished.

Imitations (A) Glass imitating malachite; (B) Glass imitating rutilated quartz; (C) Ceramics imitating turquoise
Imitations (A) Glass imitating malachite; (B) Glass imitating rutilated quartz; (C) Ceramics imitating turquoise

And when the gemologist is not around?

There are many places where gems are sold. Cities such as Governador Valadares and Teóilo Otoni, in Minas Gerais, Brazil, are centers for the sale of gemstones.

However, the gems are also sold at specific events and fairs in the jewelry market, as well as in specialized stores.

Knowing the integrity of your supplier makes it easier to buy certified gems, however, in other situations it is necessary, at least, some basic knowledge to not buy glass instead of gem.

Today, jewelry designers, jewelry authors and goldsmiths need to know the principles of gemology in order to present a reliable work to their clients.

A few years ago I witnessed a famous jeweler buy glass instead of onyx.

The results could have been disastrous if the glass had not been identified before being set in the jewel.

Even without such a high value, the simple fact that the piece was sold as onyx and had glass in its place could undermine the credibility of this jeweler.

For the experienced professional, it is easier to identify the gem without carrying out a more detailed analysis, even so, the forgeries reached worrying levels of quality, as their value is infinitely lower.

To avoid embarrassing situations or even professional and financial loss, in the absence of a gemologist, we can use some gemological resources to identify gems.

It is important to point out that any gemological analysis that is not complete has a margin of error.

Three simple and not so expensive instruments can be used for gem identification: the 10X loupe, the Chelsea filter and a flashlight.

10X magnifier, the chelsea filter and a flashlight
Three simple and not so expensive instruments can be used for gem identification: the 10X loupe, the Chelsea filter and a flashlight.

Visits to events, inside and outside Brazil, can bring many opportunities to buy gems. Another situation is visiting mining areas, which is quite common. In this situation it is very important to know how to evaluate the gems and pay a fair price for them.

This article aims to clarify the use of two basic tools that can help a lot. But, we advise you to know a little more about gemology or hire a gemologist.

A good gemology course can help a lot in these situations.

Examining a gemstone or gem


One of the most important aspects, which should be evaluated first, is the value of the gem. As in any other type of trade, gemstone prices vary by merchant and location.

Research a lot before buying. The market itself sets the price levels. When you receive a price offer far below the market – be wary, nobody performs a miracle.

Price is the first factor that can establish the legitimacy of a gem.

using magnifying glass


Goldsmith loupes are an important resource for assessing what is inside a gem. Here we are indicating a magnifying glass with 10X magnification, however there are magnifying glasses with more magnification.

Natural gemstones will always have tiny internal defects, irregular patterns and formation marks. Be wary if a gem is completely free of these irregularities.

In emeralds, for example, check for bubbles. The natural ones don't have air bubbles.

Whenever carrying out this type of analysis, the magnifying glass must be close to the eyes and the gem farther away until focus is obtained. Whenever possible, perform this analysis with the gem illuminated. 

Using the chelsea filter

chelsea filter
chelsea filter

This chelsa filter was created in the early 20th century in England, initially used at the University of Chelsea.

Its initial function was to separate the emeralds Both of you green beryls.

As in the beryl group, the chelsea filter allowed this separation, they include:

  • emeralds
  • aquamarine
  • precious beryl
  • chrysoberyl
  • spinel
  • topaz
  • some of them have shades of green

At that time, only chrome-colored beryls were considered emeralds and vanadium-colored ones were considered another type of beryl.

The mineral beryl is a cyclosilicate of beryllium and aluminum with the chemical formula Be3Al2(SiO3)6. Some varieties of beryl have been considered precious or semi-precious stones since prehistoric times. The green beryl (due to the presence of the element Cr³+ as an impurity in its crystalline structure) is called emerald, the rare red beryl is called red emerald, scarlet emerald or bixbite. Blue beryl (due to chromium and vanadium) is called aquamarine, pink beryl (due to manganese and iron) is morganite, a bright, clear yellow beryl is called golden beryl, a colorless beryl is called gochenite, and greenish-yellow (due to manganese, iron and titanium), heliodor.

As emeralds had a high value, it was important to separate them from other types of beryl by means of a simple and precise test – the chelsea filter.

At that time, beryl colored by chromium (emerald) showed a reddish hue when analyzed with the chelsea elter, which did not occur with beryl colored by vanadium.

Over time it was realized that that small instrument could separate many other natural gems from imitations.

chelsa filter
Viewed through the Chelsea filter, a true emerald will appear yellowish or reddish.

However, it is important to remember that the chelsea filter is an additional tool and should not be used as a diagnostic tool, as this requires a more complete gemological analysis. It works well for the aforementioned situations.

How the chelsa filter works

As its name says, it is a light filter.

Chelsea filter allows only certain colors, yellow-green and red to be transmitted, ie seen (filters the others).

Gemstones that do not transmit yellow-green or red colors will be seen as a dark image.

Viewed through the Chelsea filter, a true emerald will appear yellowish or reddish.

Viewed through the chelsea filter, a fake emerald will appear grayish.

Looking at a synthetic emerald with the Chelsea filter, it will look real because its composition also contains chromium and it has all the physicochemical characteristics of the natural one.

chelsea filter
Viewed through the chelsea filter, a fake emerald will appear grayish.

However, in synthetics the glow of red is more intense. More experienced gemologists recognize the synthetic because it contains a greater amount of chromium making it much more luminous.

If in doubt, further gemological tests will be required for this assessment.

synthetic blue spinel

Sometimes the chelsea filter allows you to quickly assess whether a gem is synthetic or natural as is the case with blue spinel.

There is no other blue gem with refractive index 1.72 that shows the red color reaction under chelsea filter observation, only the synthetic blue spinel.

The reason for this reaction is the presence of cobalt in the synthetic blue spinel.

In the production of synthetic spinel, two different processes can be used, however the presence of cobalt is detected, in both cases, by the red reaction. Recognizing the cobalt layer.

In synthetic topaz, for example, cobalt produces a vivid color and contributes to it being one of the most prized gems, until it is used in jewelry and the cobalt begins to flake.

Cobalt contributes to topaz green, for example, is marketed by different names, as is the case of caribbean green topaz, etc.

Since natural topaz is not naturally produced in this color, any green topaz is a cobalt-coated gem.

If you have an unknown green stone, you can easily identify it with the chelsea filter, as no other green gem will show the kind of strong reaction seen with the chelsea filter. Separating natural tanzanite from imitation.

Three types of tanzanite: 1 is a natural tanzanite, 2 is an imitation polysilicate, and 3 is a synthetic one. 2 and 3 are the most common imitations of tanzanite.

the tanzanite it is a trichroic gem. The third color comes in a golden brown to a reddish-brown hue.

In the image below we can see three types of tanzanite: 1 is a natural tanzanite, 2 is an imitation of polysilicate and 3 is a synthetic one. 2 and 3 are the most common imitations of tanzanite.

When viewed on the chelsea filter the reaction of the three is very different.

Note that 3 has an inert reaction. The luminous red reaction of the polysilicate (gem 2) is due to the agents added to achieve this imitation reaction, but you can see that the red is much brighter than the reaction of natural tanzanite (gem 1).

The same principle of luminosity occurs with alexandrites. A synthetic alexandrite will have a high luminosity effect when viewed through the chelsea filter, while natural alexandrite will have less luminosity.

tanzanite gem
Note that 3 has an inert reaction. The luminous red reaction of the polysilicate (gem 2) is due to the agents added to achieve this imitation reaction, but you can see that the red is much brighter than the reaction of natural tanzanite (gem 1).

This is due to the large amount of chromium added in the laboratory process of synthetic gems.

The images used in this article are merely illustrative and can differ greatly in shades when observed with the chelsea filter.

The important thing is to know the principles of the analysis made with this filter.

We advise you to take a gemology course to understand much more about gemstone identification.

Gemology an almost obligatory study

Our subject this month in the “gems” section is Tourmaline, one of the gems most preferred by jewelry designers and consumers alike.

But, thinking a little more about those who are still starting, studying or perfecting themselves in the study of jewelry design, we decided to open this section with some information about gemology.

You will see that gemology is an almost mandatory study for the jewelry designer.

Before talking about gemology, let's understand what a gem is.

Until a few decades ago, the name “precious stone” was used to designate diamonds, rubies, roses and emeralds, considered valuable stones because they are the most used in the production of jewelry.

Today, we know that there are other minerals, such as amethyst with stones, that can be worth more than an emerald.

There is spodumena kunzite (pink stone) which may be worth more than diamonds.

Some organic materials such as pearl and amber have also been used in personal adornments and added value to these jewels.

With so much scope and valuation of substances in the jewelry market, how is it possible to determine the value of these elements and compare them? How to know if a ruby ​​is real or is an imitation? Faced with these needs, Gemology was born.

Gemology is a specialty of geology that studies the physical and chemical aspects of materials of gemological value, whether of organic or inorganic origin, which are used as personal adornment or environment decoration.

For a material to have gemological value, it must simultaneously have beauty, rarity, tradition, fashion and durability.

Gemstones are substances that have aesthetic values ​​such as color, shape (cutting) and durability considering their characteristics and physical and chemical properties.

Gemology is also dedicated to distinguishing gems obtained by synthesis, their imitations, as well as discovering the different types of treatment used to improve their appearance and value. It also studies the origin, composition and optical properties.

It also studies the lapidation (facet cuts) suitable for each type of stone that enhances its beauty.

The study of this science is undoubtedly essential for jewelers, jewelry designers, gem traders, goldsmiths and other professionals in the sector.

The specialist in gemology is the gemologist. If you want to learn gemology, see the website of some courses.

For those interested in an academic training, the Federal University of Espirito Santo. UFES has an undergraduate course in gemology

Brazil lacks professionals with scientific training in this area.

A good guide for the study of gemology is the book “Gems of the World”.

It is important to know that an accurate gemological analysis requires adequate equipment and instruments, but gemological knowledge can help a lot in the identification of gems.

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