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

And we, the jewellery professionals, give them shapes and facets that enhance their brilliance and value when creatively applied in a jewel.

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

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

The first precious stones were probably found in riverbeds.

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

The extraction and commercialisation of precious stones had already been done for thousands of years.

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

This process has led to these natural gems increasing in price. 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 imitation stones have been perfected in their production processes.

Soon after the first fakes, gemology emerged – a science derived from crystallography that defines concrete parameters for evaluating and classifying gems.

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

Thus, when you want to buy a very valuable gem, the best way is to hire the services of a gemologist;

Precious and Semi-precious Stones

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

To understand how this change occurred, it is necessary to know a little about the history of gems. The name precious stone was used only for diamond, emerald, ruby and sapphire, known as cardinal gems, because they had ecclesiastical, devotional or ceremonial use; the other gems were called semi-precious.

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 Gems

Among the various Brazilian gems, tourmalines and the various types of beryls are very prominent.

1. Beryls

The mineral beryl is a silicate of beryllium and aluminium that has prismatic or columnar habit, with hexagonal base, hardness of 7.5-8, specific weight of 2.63-2.80. It has a vitreous lustre and can be transparent or translucent, with weak cleavage.

Pure beryl is colourless, but can be tinted by impurities; with the following colours: green beryl is called emerald (presence of ferric iron or chromium), blue beryl, 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 heliodorite, colourless beryl is goshenite.

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

2. Tourmalines

Tourmaline group minerals are boron and aluminium silicates, with variable composition due to the substitutions that can occur in their structure. The elements that commonly participate in the substitutions are Fe, Mg, Na, Ca and Li. Tourmalines exhibit prismatic habit, varying from long and thin crystals, to thick columnar, with triangular basal section, with hardness 7-7.5, specific weight between 2.9-3.2.

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

Tourmalines are divided according to their colour: dravite: brown; schorlite: black; elbaite: green; rubellite: pink; indicolite: dark blue; acroite: colourless, among others.

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

Synthetic gems

Synthetic gems are those produced in a laboratory and which have a counterpart in nature. These materials have the same chemical composition, crystal structure, physical and optical properties as their natural counterparts.

The Gemological Institute of America (GIA), the largest and most respected institution for gem research and study, describes on its website that a synthetic gem is one that is produced in a laboratory but shares all the chemical, optical and physical characteristics of a corresponding natural mineral, although in some cases, such as synthetic turquoise and synthetic opal, additional compounds may be present.

Artificial gems

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

Shah (2012) differentiates artificial gems from synthetic ones, stating that artificial gems are those that have no correspondents among natural stones, and are totally man-made; synthetic stones are crystallised or recrystallised materials, whose manufacturing method is totally or partially caused by man, but which have the same physical and chemical composition and optical properties as natural stones.

The Gemological Institute of America (GIA) cites cubic zirconia (zirconium oxide), yttrium-aluminium garnet (YAG), gallium-gadolinium garnet (GGG), fabulite (strontium titanate), and moissanite (silicon carbide) as the main artificial gems, almost all of which simulate diamond.

Imitation gems

Imitations are simulacra of natural gems, imitating their colour and appearance. Imitations are different from synthetic gems, and can be distinguished from natural and synthetic gems by their totally different physical properties and chemical composition. Imitations are mainly made of glass, paste or rhinestones, faience, porcelain and plastics, they are moulded and not cut.

What about when the gemologist is not around?

There are many places where gems are traded. Cities like Governador Valadares and Teóilo Otoni, in Minas Gerais, Brazil, are gem commercialisation hubs.

However, gems are also sold at events and fairs specific to the jewellery market, as well as in specialised shops.

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 not to buy glass instead of gem.

Today, jewellery designers, jewellery authors and goldsmiths need to know the principles of gemology to present reliable work to their clients.

A few years ago I witnessed a famous jeweller buying glass instead of onyx.

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

Even without such a high value, the mere fact that the piece was sold as onyx and had glass in its place could undermine the jeweller’s credibility.

For the experienced jeweller, it is easier to identify the gem without a more detailed analysis, even so, fakes have reached worrying levels of quality, as their value is imminently lower.

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

It is important to note 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 magnifying glass, the chelsea filter and a torch.

Visits to events, inside and outside Brazil, can bring many opportunities to buy gems. Another situation is the visit to 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

Price

One of the most important aspects, which should be evaluated first, is the value of the gem. As in any other type of trade, gem prices vary from trader to trader and locality to locality.

Do a lot of research before you buy. The market itself sets the price levels. When you receive an offer for a price far below the market – be wary, no one can work a miracle.

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

Using the magnifying glass

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

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

In emeralds, for example, check for bubbles. Natural emeralds do not have air bubbles.

Whenever you do this type of analysis, the magnifying glass should be close to your eyes and the gem should be distanced until you get the focus. Whenever possible do this analysis with the gem illuminated;

Using the chelsea filter

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

Its initial function was to separate the emeralds from the green beryls.

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

• emeralds
• sea water
• precious beryl
• crysoberyl
• spinelium
• topaz
• Some of them have green tones

At that time, only beryls coloured by chromium were considered emeralds and those coloured by vanadium were considered another type of beryl.

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

At that time, chrome-coloured beryl (emerald) had a reddish tinge when analysed with the chelsea filter, which was not the case with vanadium-coloured beryl.

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

.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 more thorough gemological analysis. It serves well for the situations mentioned.

How the chelsa filter works

As its name implies, it is a light filter.

Chelsa filter allows only certain colours, yellow-green and red, to be transmitted, i.e. seen (it filters out the others).

Gems that do not transmit the colours yellow-green or red 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 greyish.

Looking at a synthetic emerald with the chelsea filter it will appear real because it also contains chromium and has all the physical and chemical characteristics of a natural emerald.

.However, synthetic emeralds have a more intense red colour. More experienced gemologists recognise synthetic emeralds because they contain a higher amount of chromium, making them much brighter.

If in doubt, further gemological tests will be necessary 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 colour reaction under chelsea filter observation, only synthetic blue spinel.

The reason for this reaction is the presence of cobalt in 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. Recognising the cobalt layer.

In synthetic topaz, for example, cobalt produces a vivid colour and contributes to it being one of the most prized gems, until it is used in a jewel and the cobalt starts to flake off.

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

As natural topaz is not produced by nature in this colour, any green topaz is a gemstone coated with cobalt.

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

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Tanzanite is a trichroic gemstone. The third colour presents itself in a golden brown to a reddish-brown tone.

In the following image we can see three types of tanzanite: 1 is a natural tanzanite, 2 is a polysilicate imitation 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) occurs because of the agents added to obtain this imitation reaction, but you can see that the red is much more luminous than the reaction of natural tanzanite (gem 1).

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

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

The images used in this article are for illustrative purposes only and may differ greatly in colour 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 gem identification.

Gemology an almost obligatory study

Our subject this month in the “gems” section is Tourmaline, one of the gems of great preference for jewellery designers and consumers.

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

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

Before talking about gemology let’s understand what gem is.

Until a few decades ago, the name “gemstone” was used to designate the diamond, ruby, sapphire and emerald, considered valuable stones because they were the most used in jewellery production.

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

There is kunzita spodumena (pink stone) that can be worth more than diamonds.

Some organic materials such as pearl and amber have also been used in personal adornment and added value to such jewellery.

With such a wide range and valuation of substances in the jewellery market, how is it possible to determine the value of these elements and compare them? How to know if a ruby is real or an imitation? Gemology was born in response to these needs.

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

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

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

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

It also studies the cutting (facet cuts) appropriate to each type of stone that enhances its beauty.

The study of this science is undoubtedly indispensable for jewellers, jewellery designers, gem merchants, 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.
www.abgm.com.br
gemology.ibgm.com.br/school/
www.joia-e-arte.com.br/Cursos/cursoigemologia

For those interested in academic training, the Federal University of Espirito Santo. UFES has an undergraduate programme in gemology.
www.gemologia.ufes.br.

Brazil lacks professionals with scientific training in this area.

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

It is important to know that for an accurate gemological analysis, adequate equipment and instruments are needed, but gemological knowledge can help a lot in gem identification.