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.
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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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