A QUICK GUIDE FOR BEGINNERS
LOKE HUIYING
B.Sc. (Pharm), FGA (London), CDG (HRDAntwerp), AJP (GIA)
10 Steps to Gem Identification 2
Intro-
duction
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 colour-
less 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 be-
tween the 4Cs of diamonds and gemstones is that colour plays
the most important part, followed by clarity, then carat weight
and cut.
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
jadeite carving.
3 10 Steps to Gem Identification
Ruby from Thailand
Gemstone
Origin
Different gemstones are formed under different geological
In this e-book, we would like
to help you understand the
value of gemstones through
conditions. Some gems are formed under high temperature
the 10 steps to gem
and high pressure, e.g. diamonds. Some gems are formed under
magmatic or metamorphic conditions, e.g. corundum (ruby and identification. In the gem
sapphires). Others could be formed under pegmatitic condition,
e.g. tourmalines. Gemstones from different locality often appear industry, it is very
slightly different due to the chemical composition of trace
elements. Sometimes, they have distinct internal characteris-
important that you know
tics that give the gem a special ‘touch’. One such example is the
what you are buying, even
Kashmir sapphire, which can be found in the deep mountains
of Kashmir. These blue sapphires contain wispy inclusions that before bargaining for the
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 right price. We hope that this
is much higher, as compared to blue sapphires that are from Sri
Lanka. e-book is “Where Gemology
Comes Alive” for you!
Sapphire from Sri Lanka
10 Steps to Gem Identification 4
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.
5 10 Steps to Gem Identification
Gem
Materials
Crystalline Gemstones Non-Crystalline Gemstones
Single Crystals Crystal Aggregates Amorphous
7 Crystal Systems2 Polycrystalline and Organic3 Inorganic
and Twin Crystals Cryptocrystalline
E.g. Amber, jet E.g. Opal, obsidian
E.g. Diamond, E.g. Agate, jadeite,
peridot, garnet, nephrite, malachite,
quartz, zircon and turquoise, lapis
tourmaline. lazuli.
1
Gemology – the study of gemstones.
2
7 Crystal systems – different systems have different crystal symmetries that give different optical characteristics.
3
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 6
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 Sapphire
Multi-Colour
Red
Ruby
Blue
Tourmalines Sapphire and Diamond Ring
7 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 8
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
9 10 Steps to Gem Identification
doubling effect in zircon
zebra stripe in amethyst
quartz crystal 2-phase inclusion
Natural
10 Steps to Gem Identification 10
Typical inclusion of
Synthetic Stones
flux inclusion in flux melt synthetic emerald
vernueil flame fusion synthetic ruby
wispy veil in flux-melt synthetic emerald flux-melt synthetic emerald
curved striations in vernueil flame
fusion synthetic ruby
Synthetic
nail-head spicules in flux-melt
synthetic emerald
hydrothermal synthetic emerald chevron growth markings in
hydrothermal synthetic emerald
11 10 Steps to Gem Identification
opal imitation triplet lustre difference between
garnet and paste
garnet-topped doublet
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 12
Step 5
Measure Refractive Index
This is a diagnostic test, which is a vital step for any gem- Based on its optic characteristics, the testing results will
ologist to identify a gem material. In this test, we require vary accordingly. Most of the time, the RI reading can
a refractometer, monochromatic light and contact liquid. allow us to immediately know the identity of the material.
Every gem material has its distinct refractive index (RI).
Testing Tools
fibre optic light
refractometer
RI liquid
13 10 Steps to Gem Identification
Gem Material Testing Results Examples
Technique
Faceted, crystalline Total Internal Single Refractive, Spinel, garnet, glass
Reflection one shadow edge
Double Refractive, Sapphire, ruby, tourmaline,
Two shadow edges emerald, peridot
Cabochon, crystalline ‘Distant vision’ Spot reading Cat’s-eye, star sapphire,
cat’s eye tourmaline
Cabochon, polycrystalline cabochon jadeite,
turquoise, rhodochrosite,
rhodonite, agate
Carvings jadeite, nephrite
Organic Precautions – coral, amber, ivory
Organic materials are
porous and permeable.
The RI liquid may stain
or damage these
materials.
10 Steps to Gem Identification 14
Step 6
Observe Absorption Spectrum
The equipment used for observing absorption spectrum is the prism spectro-
scope 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.
15 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 observation under
London dichroscope
dichroic colours of ruby under the two different types of 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 16
Step 8
Other Optical Properties
The polariscope can be used to test transparent and
some translucent gem materials. This is not a diag-
nostic 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 behav-
ior. 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
17 10 Steps to Gem Identification
Type of Material Observation Examples
Garnet, spinel, natural glass, paste,
Optically Isotropic Stone remains dark through 3600
diamond, opal
SR positions (9 positions) Garnet and spinel samples
Stone goes light & dark 4 times Emerald, ruby, sapphire, topaz,
Optically Anisotropic
through 3600 tourmaline, quartz, tanzanite
DR positions (9 positions) quartz sample
Polycrystalline Stone stays light through 3600 Jadeite, nephrite, agate, doublets
polycrystalline positions (9 positions) Agate and jadeite samples
Natural glass, paste, almandine
Stone shows anomalous extinction
Amorphous or strained anisotropy garnet, amber, diamond, synthetic
effect
spinel.
08 amorphous positions (9 positions) amber sample
10 Steps to Gem Identification 18
Ultraviolet (UV) radiation produces fluo-
rescence effects in some materials. Some
laboratories use UV spectrophotometers
9
to measure the absorption of UV light by
some gem materials. This test is not diag-
nostic, but can aid in identification. It can
Step
be used on mounted stones, strung beads
or a parcel of loose gemstones. 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 Inert or typically chalky white
Cubic Zirconia Weaker than SW or inert Yellow to dull apricot-orange
Synthetic Spinel Inert Chalky, blue/green
Zircon Brownish-yellow Inert
Source: Gem-A Foundation
Picture of diamonds under LWUV Picture of synthetic spinel sample
Picture of synthetic spinel under LWUV Picture of synthetic spinel under SWUV
19 10 Steps to Gem Identification
Step 10
Advance Testing Techniques
Generally, it is easy to identify gem materials from the 10 steps value differs greatly between a heated sapphire and a natural,
described above. However, in the market, the difficulty is very non-heated sapphire, given that both has similar quality in size,
often not about testing for the identity of the gemstones. The colour and clarity.
difficulty is to identify whether the gem material has been
treated in any way. For example, heat treatment in ruby and sap- Other scenarios could be the identification of treated jadeite,
phire. It is important to identify the treatment in this case as the identification of synthetic diamonds and identification between
saltwater pearls and freshwater pearls.
Advanced Testing Principle Examples
X-ray radiography Different materials have varying Detect glass fillings in fissures within diamonds and
degrees of transparency ruby.
X-ray luminescence Fluorescence or phosphorescence of a Identification between freshwater pearls and saltwater
materials when exposed to X-rays pearls.
source: http://www.ssef.ch/education/advanced-training-courses/pearls/
X-ray diffraction X-ray diffracted into the characteristic Used to identify natural pearls.
pattern of the material.
source: http://documents.htracyhall.org/
Infrared spectrometer Using infrared radiation to measure Detecting polymer impregnation in treated jadeite
absorption in materials known as ‘B-jade’.
Raman spectrometer Re-emission of energy when a very Used to identify inclusions within a gemstone.
strong beam of light (UV, visible light
or IR) is absorbed by a substance.
Cathodoluminescence An electron beam is used to stimulate Detect growth patterns within natural and synthetic
visible light fluorescence. diamond
natural CVD
Source: Natural - http://blogs.scientificamerican.com/guest-blog/some-facets-of-the-geol-
ogy-of-diamonds/
CVD - http://www.iabrasive.com
10 Steps to Gem Identification 20
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 labora-
tory, 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 recom-
mend that you must bring along.
Finally, feel free to contact us if you have any questions
about gemology and gem identification.
21 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.
Our contact details
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Email: info@gem.com.sg
Website: fareastgem.institute
THE GEM MUSEUM
222 Queen Street
#02-02
Singapore 188550
Tel: +65 6734 3172
Email: contact@thegemmuseum.gallery
Website: thegemmuseum.gallery
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