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A QUICK GUIDE FOR BEGINNERS

LOKE HUIYING

B.Sc. (Pharm), FGA (London), CDG (HRDAntwerp), AJP (GIA)


10 Steps to Gem Identification

2

Introduction

Gemstones are beautiful, rare, valuable and very frequently quite ‘mysterious’. When we see a beautiful piece of gemstone that catches our attention, we want to know what it is and its value. Gemstone Identity

Before we can know the value of a piece of gemstone, we need to first be confident about its identity. The value of a piece of red ruby can be very much higher than a piece of red garnet. The price of a diamond is very different from the price of a colourless quartz.

Gemstone Quality

Once we know the identity of the stone, we have to evaluate the quality of the stone. In general, we consider the 4Cs (just like diamonds!) – Carat, colour, clarity, cut. What is different between the 4Cs of diamonds and gemstones is that colour plays the most important part, followed by clarity, then carat weight and cut.

Jadeite carving

Other gem materials such as pearls, jadeite-jade and amber have a very different set of criteria for determining its quality. For example, apart from colour, the transparency, texture and polish are important considerations when we evaluate the quality of a jadeite carving.


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10 Steps to Gem Identification

Ruby from Thailand

Gemstone

Origin

Different gemstones are formed under different geological conditions. Some gems are formed under high temperature and high pressure, e.g. diamonds. Some gems are formed under magmatic or metamorphic conditions, e.g. corundum (ruby and sapphires). Others could be formed under pegmatitic condition, e.g. tourmalines. Gemstones from different locality often appear slightly different due to the chemical composition of trace elements. Sometimes, they have distinct internal characteristics that give the gem a special ‘touch’. One such example is the Kashmir sapphire, which can be found in the deep mountains of Kashmir. These blue sapphires contain wispy inclusions that give it a velvety appearance. Due to the nature of the mining, these sapphires are very rare on top of its beauty. Thus the value is much higher, as compared to blue sapphires that are from Sri Lanka.

In this e-book, we would like to help you understand the value of gemstones through the 10 steps to gem identification. In the gem industry, it is very important that you know what you are buying, even before bargaining for the right price. We hope that this e-book is “Where Gemology Comes Alive” for you!

Sapphire from Sri Lanka


10 Steps to Gem Identification

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Step

1

General Observation of Gem Material

When we hold a gem in our hands, we have to be able to know what the nature of gem material is. Following shows a simple diagram on the classification of gemstones in gemology. Understanding the classification of gem materials helps us to make our identification much easier. It also helps us to decide the gemological equipment to use for identification.


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10 Steps to Gem Identification

Gem Materials

Crystalline Gemstones

Single Crystals

Crystal Aggregates

7 Crystal Systems2 and Twin Crystals

Polycrystalline and Cryptocrystalline

E.g. Diamond, peridot, garnet, quartz, zircon and tourmaline.

E.g. Agate, jadeite, nephrite, malachite, turquoise, lapis lazuli.

1 2 3

Non-Crystalline Gemstones

Amorphous

Organic3

Inorganic

E.g. Amber, jet

E.g. Opal, obsidian

Gemology – the study of gemstones. 7 Crystal systems – different systems have different crystal symmetries that give different optical characteristics. Organic materials also include pearls, corals and petrified wood. These materials come from living organisms, but may have been replaced by crystalline materiaHence, it is not classified above.


10 Steps to Gem Identification

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Step

2

Colour Observation Every type of gemstone has its distinct shade of colour due to its optical characteristics. Gemstones have a primary colour and a secondary colour. For example, ruby has a primary colour of red and a secondary colour of pink, orange or brown. As you keep making conscious observation of gemstones, you will notice that your eyes become more and more sensitive to the secondary colours in a gemstone. The shade of colour can also potentially be the main determination of the value of the gem material.

Colourless Topaz

Green Emerald

Yellow Red Ruby

Tourmalines

Multi-Colour

Sapphire

Blue Sapphire and Diamond Ring


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10 Steps to Gem Identification

Adamantine

Sub-adamantine

Bright Vitreous

Rough Diamonds

Zircon

Spinel

Polished Diamonds

Sphene

Topaz

Step

3

Observe Lustre Lustre is the surface reflection and surface condition of a gem material. By observing the lustre, you can have a good idea of the hardness, reflectivity and refractive index of the stone.

Vitreous

Dull Vitreous

Resinous

Opal

Fluorite

Amber

Citrine (Quartz)

Calcite

Pearly


10 Steps to Gem Identification

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Step

4

Note Internal and External Characteristics In gemology, observation of the internal and external characteristics of a gemstone is crucial in the identification of the gem material. Internal characteristics, also commonly known as inclusions, are often thought a undesirable as it affects the value of the gem. However, understanding and knowing the types of inclusions can help us to identify gems and differentiate among natural, synthetic and composite materials.

10x loupe and microscope are the two main equipment used to make observations of internal and external characteristics.

Typical inclusions of

natural gemstones fingerprint in blue sapphire

horsetail inclusion in demantoid garnet

lily-pad in peridot

centipede inclusion in moonstone


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10 Steps to Gem Identification

doubling effect in zircon

zebra stripe in amethyst

quartz crystal

2-phase inclusion

Natural


10 Steps to Gem Identification

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Typical inclusion of

Synthetic Stones

flux inclusion in flux melt synthetic emerald

vernueil flame fusion synthetic ruby

wispy veil in flux-melt synthetic emerald

curved striations in vernueil flame fusion synthetic ruby

flux-melt synthetic emerald

Synthetic

nail-head spicules in flux-melt synthetic emerald hydrothermal synthetic emerald

chevron growth markings in hydrothermal synthetic emerald


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opal imitation triplet garnet-topped doublet

10 Steps to Gem Identification

lustre difference between garnet and paste

side view of triplet

Typical inclusion of

Synthetic Stones

Typical Characteristics of composites

sapphire and synthetic sapphire doublet

joint plane between sapphire and synthetic sapphire doublet


10 Steps to Gem Identification

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Step

5

Measure Refractive Index This is a diagnostic test, which is a vital step for any gemologist to identify a gem material. In this test, we require a refractometer, monochromatic light and contact liquid. Every gem material has its distinct refractive index (RI).

Based on its optic characteristics, the testing results will vary accordingly. Most of the time, the RI reading can allow us to immediately know the identity of the material.

Testing Tools

fibre optic light

refractometer

RI liquid


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10 Steps to Gem Identification

Gem Material

Testing Technique

Results

Examples

Faceted, crystalline

Total Internal Reflection

Single Refractive, one shadow edge

Spinel, garnet, glass

Double Refractive, Two shadow edges

Sapphire, ruby, tourmaline, emerald, peridot

Spot reading

Cat’s-eye, star sapphire, cat’s eye tourmaline

Cabochon, crystalline

Cabochon, polycrystalline

Carvings Organic

‘Distant vision’

Precautions – Organic materials are porous and permeable. The RI liquid may stain or damage these materials.

cabochon jadeite, turquoise, rhodochrosite, rhodonite, agate

jadeite, nephrite

coral, amber, ivory


10 Steps to Gem Identification

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Step

6

Observe Absorption Spectrum The equipment used for observing absorption spectrum is the prism spectroscope and/or diffraction grating spectroscope. This is a diagnostic test as the absorption band for each type of gemstone is different and distinctive.

Prism spectroscope

diffraction grating spectroscope

Here are some examples of absorption spectrum:

spectrum of ruby

spectrum of sapphire

spectrum of emerald

spectrum of jadeite-jade

spectrum of almandine garnet

spectrum of red glass

spectrum of blue glass coloured by cobalt

Source: Gem-A Foundation textbook on spectrum images.


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10 Steps to Gem Identification

calcite and London dichroscope

using the London Dichroscope

Step

7

Observe Pleochroism Pleochroism is an optical characteristic of crystalline gem materials, where the material appear to have completely different colours when viewed from different directions. Only coloured, anisotropic (DR) stones can exhibit this optical property. Below is an example of observation of dichroic colours of ruby under the two different types of

observation under London dichroscope using synthetic verneuil flame fusion ruby

dichroscope:

observation under calcite dichroscope with the same synthetic verneuil flame fusion ruby as above.


10 Steps to Gem Identification

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Step

8

Other Optical Properties The polariscope can be used to test transparent and some translucent gem materials. This is not a diagnostic test, but it can be used to test mounted stones, strung beads or a parcel of loose gems all at once. This equipment is fitted with two polarizers (just like the ones for sunglasses), in ‘crossed’ position. The gem is placed in between the two polarizers and rotated to observe its behavior. The results depends on the type of material, whether it is optically isotropic, or optically anisotropic, polycrystalline or amorphous. This test is not useful for opaque materials.

No Extinction effect Polarizer position 3

Extinction effect Polarizer position 1 (crossed polars)

polarizer position 2


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10 Steps to Gem Identification

Type of Material

Observation

Examples

Optically Isotropic

Stone remains dark through 3600

Garnet, spinel, natural glass, paste, diamond, opal

Optically Anisotropic

Stone goes light & dark 4 times through 3600

Emerald, ruby, sapphire, topaz, tourmaline, quartz, tanzanite

Polycrystalline

Stone stays light through 3600

Jadeite, nephrite, agate, doublets

Amorphous or strained anisotropy

Stone shows anomalous extinction effect

Natural glass, paste, almandine garnet, amber, diamond, synthetic spinel.

SR positions (9 positions)

DR positions (9 positions)

polycrystalline positions (9 positions)

08 amorphous positions (9 positions)

Garnet and spinel samples

quartz sample

Agate and jadeite samples

amber sample


10 Steps to Gem Identification

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Ultraviolet (UV) radiation produces fluorescence effects in some materials. Some laboratories use UV spectrophotometers to measure the absorption of UV light by

Step

some gem materials. This test is not diagnostic, but can aid in identification. It can be used on mounted stones, strung beads or a parcel of loose gemstones.

9

Observe Fluorescence

Typically, two energy UV light are used: • Long wave UV with principal wavelength of 365nm • Short wave UV with principal wavelength of 254nm This test is useful for the following materials: Material

LWUV

SWUV

Diamond

Often bluish-white

Weaker than LW

Colourless glass (paste) Inert

Cubic Zirconia

Synthetic Spinel

Zircon

Weaker than SW or inert Yellow to dull apricot-orange

Inert

Brownish-yellow

Picture of diamonds under LWUV

Inert or typically chalky white

Picture of synthetic spinel under LWUV

Source: Gem-A Foundation

Chalky, blue/green

Inert

Picture of synthetic spinel sample

Picture of synthetic spinel under SWUV


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10 Steps to Gem Identification

10

Step

Advance Testing Techniques Generally, it is easy to identify gem materials from the 10 steps described above. However, in the market, the difficulty is very often not about testing for the identity of the gemstones. The difficulty is to identify whether the gem material has been treated in any way. For example, heat treatment in ruby and sapphire. It is important to identify the treatment in this case as the

value differs greatly between a heated sapphire and a natural, non-heated sapphire, given that both has similar quality in size, colour and clarity. Other scenarios could be the identification of treated jadeite, identification of synthetic diamonds and identification between saltwater pearls and freshwater pearls.

Advanced Testing

Principle

Examples

X-ray radiography

Different materials have varying degrees of transparency

Detect glass fillings in fissures within diamonds and ruby.

X-ray luminescence

X-ray diffraction

Infrared spectrometer Raman spectrometer

Cathodoluminescence

Fluorescence or phosphorescence of a materials when exposed to X-rays

X-ray diffracted into the characteristic pattern of the material.

source: http://documents.htracyhall.org/

Identification between freshwater pearls and saltwater pearls.

source: http://www.ssef.ch/education/advanced-training-courses/pearls/

Used to identify natural pearls.

Using infrared radiation to measure absorption in materials

Detecting polymer impregnation in treated jadeite known as ‘B-jade’.

An electron beam is used to stimulate visible light fluorescence.

Detect growth patterns within natural and synthetic diamond

Re-emission of energy when a very strong beam of light (UV, visible light or IR) is absorbed by a substance.

Used to identify inclusions within a gemstone.

natural

CVD

Source: Natural - http://blogs.scientificamerican.com/guest-blog/some-facets-of-the-geology-of-diamonds/ CVD - http://www.iabrasive.com


10 Steps to Gem Identification

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Conclusion We hope that you have learnt something about testing of gemstones through this e-book. Notice that the first three steps are observations by naked eye, fourth to sixth steps are diagnostic tests with simple equipment (some handheld), seventh to ninth steps are non-diagnostic test, but may give very good indications of the identity. Final step of the testing procedure described in this e-book can only be carried in a gemological laboratory, as it involves high-energy rays such as X-rays. Only a qualified technician or gemologist is allowed to operate these advanced equipment. In the field/market, there are some tools that we recommend that you must bring along. Finally, feel free to contact us if you have any questions about gemology and gem identification.


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10 Steps to Gem Identification

About the Author Ms. Loke Huiying is the Director of Far East Gem Institute and Founder of The Gem Museum. She has been training jewellery professionals and business owners in the subject of gemology since 2009. She is also actively involved in the development of gemological programs for gems and jewellery business owners. Currently, she is helping her clients to start their business in the gems and jewellery industry through a 4C method – Clarity, credibility, connection, commitment. She is also in the process of writing her first book, Hidden Gems for the entrepreneurs entering this industry. Ms. Loke strongly believes in education and building strong relationships with people.


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10 Steps to Gem Identification