Abbey N. Zwach
Every gemstone in the world
holds its own unique beauty, rarity, and identity. Gem identification is a
process of observing and testing a gemstones chemical properties and
characteristic structure. This process requires gemological procedures and a
well trained eye.
There are many cases in which
identifying a gemstone is a very important task in order to avoid financial loss
and in order to hold a superior reputation. If you are a buyer or a seller of
gemstones you need to be able to accurately assess the value of the product and
determine if they are genuine or synthetic stones. Appraisals for insurance
value and trade in value are required to disclose treatments and enhancements,
and in order to provide this information you will have to be able to identify
the stone first and its treatments. General Observation along with the aide of
magnification is the first step to take in identifying a gemstone, followed by
instrumental testing which requires the use of tools such as the refractometer.
Step #1: General Observation:
General observation is the
first key step in the gemstone id process. By using the unaided eye and 10
power magnification to determine the visible characteristics you are able to
take a large step in the right direction of identifying the stone. There are
several steps in this process that will dramatically narrow your possibilities;
some of the most helpful steps are finding the stones Tone, Hue, and
Transparency and if it displays a Phenomena.
In order to successfully
visually analyze a stone start by using a neutral colored background, a properly
lighted environment, and consistency in your procedure. There are a few tools that
will aide in this particular process, a gemstone cloth, incandescent light
source, ultra violet light source, daylight equivalent lighting, a 10 power
loupe, and tweezers will be needed. Although the general observation process is
very helpful it will not complete the identification of a stone, you will also
need to perform and analyze instrumental testing with the use of gemology
tools. Make sure to record your test results along the way, when you have
finished you will need to evaluate your results and search out the possible
gemstones that would be applicable.
Color: A stone needs to
be examined in 3 directions, face up so the top know as the table is facing you,
face down so that the bottom known as the pavilion and culet is facing you, and
a profile view where you will see the side of the stone where the girdle is
visible. Examine the stone to determine what color hue it is and to determine
the tone level ranging from very light to very dark. Color charts displaying
the range of hues found in colored gemstones are helpful aides to use when
determining the correct hue seen in a stone.
transparency range from opaque to transparent. Opaque describes where a stone
is unable to transmit any light through it. Transparent describes a stones
transparency being able to transmit light so that objects viewed through the
stone are sharp and visible.
Cut: Cut style of a
stone can be a small indicator of the possibilities of its identity, due to the
fact that certain stones tend to be cut in particular styles. Some of the more
common cut styles you will see include faceted, cabochon, cameo, bead, and
tumbled. Faceted stones come in a variety of shapes, the most common being
round. There are different styles in which a stone is faceted, terms like
brilliant, step cut, and checkerboard are some of the more popular faceting
styles seen in today’s market. Any shape beyond the shape of round is
considered a “fancy cut” stone. Some of the more common fancy cut stones
include oval, pear, princess, emerald cut, marquise, antique, heart, trillion,
Phenomena: Being able to
observe optical effects in a stone indicates that it displays phenomena. An
optical effect will appear to float inside or outside the gems body color, this
phenomena is caused by how the gemstones structure interacts with light. These
types of special effects will appear to the observer’s eye as a shimmer, glow,
flash, change of color, or even as a moving band of light. Knowing what type of
phenomena is occurring can help considerably narrow your possibilities in
identification. Common phenomenal effects include asterism, color change, play
of color, chatoyancy, and orient. Phenomenal stones are very appealing in that
they add such a rare beauty and captivating effect to a stones overall
Luster: Luster is
described by the quality and intensity of a materials surface in reflective
light. When judging luster reflect light off of the area of the stone
that has the best polish. Levels of luster range from Adamantine and
Metallic to Dull and Waxy.
separation of white light into spectral colors is called dispersion; the visible
display of this is called fire. When separating diamond from its simulants,
detecting dispersion is an important ability to have. Using a penlight or
other source of concentrated light illuminate the stone and examine the amount
of fire and determine if it is weak, moderate, strong, or extreme. The strength
of a stones fire will help determine the possibilities of what your stone may
refers to the weight of a stone compared to its size. By holding a stone
in your hand and judging its heft will help indicate if the stone will have
a low or a high specific gravity. Stones made of amber or plastic tend
to have a low heft.
stones are made up of two or more materials which are usually cemented or fused
together. Assembled stones are referred to as doublets and triplets and can be
made of both natural and synthetic counterparts. The stones girdle is the first
place to check when testing for an assembled stone. To detect for indications of
being an assembled stone use a penlight and magnification, look for
characteristics such as luster differences between the different materials, the
red ring effect, or separation planes of colored or colorless cement. The red
ring effect refers to when a stone is turned faced down and a red ring along the
outer part of the stone is visible when light is directed onto the stone. The
red ring effect is a common way to identify a large majority of doublet
Step #2: Instrumental Testing
Accurately identifying a
gemstone is a vital skill to have if you are buying or selling colored
gemstones. Each mineral species of stones hold their own unique optical and
physical properties, scientific data is needed to prove these properties in
order to make a positive identification. In order to come up with the stones
optical and physical properties and determine which mineral species they belong
to, there are several gemological tests that need to be performed. Becoming
familiar with how to use the testing equipment is a key for success in gem
identification. By keeping your stone free of lint and oils will provide more
accurate results during testing, a lint free cloth should be used to clean the
stone between each test. Some of the most important test to conduct will be
using the microscope and loupe, refractometer for refractive index, Chelsea
filter, and a polariscope.
Microscope: When using a
microscope it is important to make sure your stone is clean. Using a gem cloth
to clean the stone before each test is important to remember since oils and dirt
from our own fingers could easily cause a mistaken identity. It takes time to
become familiar with a microscopes many features. When using a microscope there
are several lighting techniques like darkfield or brightfield illumination,
diffused, polarized, and reflected lighting; different types of lighting are
used in order to find particular clarity characteristics. The microscope itself
has several adjusting components like the baffle and iris, focus control knob,
and left and right ocular, these parts can be adjusted to fit your vision and to
focus on the part of the stone you are viewing.
One of the many benefits a
microscope will offer is being able to detect and view the clarity
characteristics also known as inclusions. These inclusions are the key to
separating genuine from synthetic gemstones. Inclusions can be unique to one
mineral species giving us the key to their identification. Clarity
characteristics also help detect treatments and enhancements, and sometimes even the
origin of the stone. Some of the common inclusions seen in genuine stones
include clouds and fingerprints, needles, crystals, and silk.
Loupe: Using a 10
power loupe is a requirement in stone identification, one with a triplet
lens will make it easier to use the loupe. Get yourself acquainted
with using a loupe and a tweezers at the same time, it is important to be
able to quickly pick up a stone and view it under a loupe. A loupe
will help in finding important information about the stone such as doubling,
surface characteristics, and inclusions.
Refractive index refers to the measured amount of changes in the angle and speed
of light as it passes through a gem. By using a pin tip size amount of
refractive index fluid and a refractometer is how you obtain this measurement.
Once the RI is found it should be compared to a gem property chart in order to
determine the possible gem species the stone may be.
polariscope is used in order to determine if a stone is singly refractive,
doubly refractive or an aggregate. The polariscope will also determine the optic
figure of a stone, if a stone has one optic axis it will be uniaxial and if it
has two optic axis’ it would be considered biaxial. In a double refractive
stone the optic axis refers to the direction in which light slows down and is
refracted. Only transparent to translucent type stones can be accurately tested
by using a polariscope.
Dichroscope: Using a
dichroscope on double refractive stones will determine if the gem displays
pleochroic colors. Gems can display separate colors within a single stone, the
colors shown are caused by the way light travels through the crystal structure
and interacts with possible trace elements within the stone; this effect is
called pleochroism. There are two types of pleochroism; when two different body
colors are shown it is dichroism and when three different body colors are shown
it is called trichroism. A dichroscope is an essential tool since it can be
used on both loose and mounted semitransparent to translucent stones. In order
to use the dichroscope properly the light source should be white light and able
to focus directly into the dichroscope.
Ultra Violet Light Source:
A gems reaction to UV (Ultra Violet) light will determine if it contains
fluorescence or phosphorescence. In some cases the strength and the color of
the fluorescence will be a great indicator of the stone species or if it’s
genuine or synthetic material. UV light sources are available in smaller and
more affordable hand held models or in larger type models that have the option
of controlling the amount of energy with short wave and long wave settings.
Keep stones clean and free of lint and oils by using a lint free gem cloth, the
presence of these can affect the stones fluorescence.
Spectroscope: Each gem
has its own distinct way of how it absorbs light; a spectroscope is used to
identify each stones unique spectrum pattern. A stones chemical composition and
crystal structure will determine what part of visible light it will absorb
influencing the color of the stone. Absorption spectrums usually consist of
dark lines or bands and dark areas referred to as a cutoff. The placement of
these lines and bands on the scale which represents the range of visible light
will help determine the mineral species the stone belongs to.
Chelsea Filter / Color
Filter: Transition elements like chromium and cobalt can cause some parts
of visible light to be absorbed determining the color of the stone. A color
filter or also known as a Chelsea filter is a tool used to detect stones
containing these transitional elements. The Chelsea filter is extremely helpful
when separating several types of synthetic stones from their natural
Heavy Liquids: Each
stone has its own unique specific gravity, which is the ratio of the weight of
the stone compared to the weight of an equal volume of water. Heavy liquids are
liquids that have a known specific gravity, they typically are available in sets
of five to six separate liquids each with their own SG (specific gravity)
usually ranging from 2.57 to 3.32. If a stone is placed in heavy liquid and it
floats, the SG of the stone should be close or lower then the liquid that it is
placed in. If a stone sinks in the heavy liquids it is an indicator that the
stone’s SG is higher then the liquid it was placed in. Make sure to
follow all safety instructions when using heavy liquids since they can be
hazardous and could cause harm if not used properly.
Diamond Tester: Each
species of stones conducts heat at different rates, this is called thermal
conductivity. Using a diamond tester will help determine the different rates of
thermal conductivity in diamonds and most of its simulants. Stones like
moissanite require using a tester specifically made for separating diamond from
moissanite. Diamonds conduct heat at a higher rate compared to many of its
simulants, a tester is able to detect the different rates at which heat is being
conducted therefore helping to identify a simulant from a genuine diamond. When
using a diamond tester there are several things to keep in mind in order to get
accurate results, make sure to closely follow a diamond testers instructions
that are included with the unit. Factors that could affect your results include
un cleaned stones, a slight touch of the metal it is mounted in, not enough time
between each test, so make sure to learn the procedure and practice with already
Reference Guide: There
are several publications that act as great aides in the gem identification
process. The 3rd edition of “Gem Identification Made Easy” is a
great book to keep on hand. This book includes Refractive Index and Specific
Gravity tables, step by step instructions on using gemological tools, helpful
hints in spotting synthetics, and much more. In order to avoid costly mistakes
a reference book is a great tool to have.
There are additional test that
can be done to separate and identify synthetic and genuine gemstones. A magnet
test can be done to help narrow the possibilities of your stone since only
certain stones contain iron making them attracted to magnetism. There are also
tests that are considered destructive to the material you are testing. The
hardness test would be considered a destructive test. By using a tool called a
hardness point tester you are able to scratch the surface of the gemstone to
determine its hardness in comparison to the Mohs harness scale. A hot point can
be used to test for stones that you are suspicious of the possibility of it
being impregnated with plastic, wax, or even oils. When a hot point is touched
on the surface the impregnated material will appear to sweat out and be visible,
this test is considered a destructive test. Although destructive testing will
help in identifying some stones it is not recommended on transparent faceted
gemstones and should only be used with the consent of the stones owner.
Synthetic and Imitation Gemstones:
Synthetic and imitation gems
flood the market place. They have a lot of positive benefits like
affordability, striking color, and an ample supply. Unfortunately due to
advancements in technology telling genuine apart from synthetic will require
careful examination. Separating genuine from synthetic stones can be a hard
task; luckily the characteristics they possess are our keys to their
identification. When buying or selling gemstones, it is crucial to be able to
detect whether the material you have is genuine or synthetic stones. A mistaken
identity of a synthetic stone could be a costly mistake and could diminish your
synthetic stone is created by man and has basically the same crystal structure,
chemical composition, and properties as its natural counterpart.
material that looks like a natural gem but is made of a completely different
material of either unnatural or natural product.
Most processes used to
create synthetic gems tend to create distinctive features within the
gemstone that help separate them from being a genuine stone. It is important
to become familiar with the clarity characteristics common in synthetic
stones. Keep yourself up to date with the constantly evolving methods
of laboratory creating gemstones. Magnification will be the key tool
in finding these inclusions in order to positively identify a stone as being
genuine or synthetic.
The two types of processes used
to grow synthetic stones are called the melt process and the solution process.
Melt processes are done by melting chemical mixtures then having the melt
recrystallized, these processes are called skull melt, pulling, and the more
common of flame fusion. The solution processes tends to be more expensive to
create and takes a longer time to manufacture, this process is done by growing
the crystal from a chemical mixture that is controlled by pressure and high
temperatures creating gems that closely resemble their natural counterpart.
Common names for the stones created by a solution process include flux grown,
hydrothermal growth, and seed crystal growth. Solution process inclusions will
usually be harder to spot since they can look very similar to a natural
Common Characteristics and
Inclusions found in Synthetics:
Curved Growth: Unlike
the angular growth seen in natural corundum a flame fusion created stone will
create what is called curved striae. Curved striae is curved growth patterns
seen within the stone, this type of growth is easier to view when using diffused
lighting. Some synthetic stones like a Synthetic Star Corundum will have eye
visible curved growth pattern making it very easy to identify, be careful not to
mistake polishing marks on the surface for curved growth within the gemstone.
Flux: Flux inclusions
are seen in synthetic stones that are created by using the flux growth process.
These type of inclusions come in many shapes and forms and range from very
coarse with high relief to colorless and possibly having shapes that resemble
those of genuine inclusions. Rod shape and liquid like shapes inclusions in
colors of white, yellow, or even brown are common to see within a flux grown
Gas Bubbles: Be careful
when using a gas bubble as a key indicator for identifying synthetic stone.
Depending on the nature of the gas bubble will indicate its possibilities of
being from a melt process synthetic. Gas bubbles found in synthetic gemstones
tend to be round in shape and may come in large strings or groups of multiple
gas bubbles. Usually if a gas bubble is found within a 2 or 3 phase inclusion it
would be considered a genuine stone. If a gas bubble is found alone it
typically would indicate synthetic, but be careful since the natural glass
moldavite will display gas bubble inclusions that are perfectly round and found
alone without other inclusions.
manufactured by using solution type processes will leave behind remnants of the
containers they are grown in called crucibles. The material seen in a stone if
referred to as a platelet, usually made of platinum or gold. Platelets tend to
resemble metallic triangular or hexagonal shapes.
Fingerprint Like Inclusion:
Flux grown synthetics will show inclusions that resemble a fingerprint
pattern, like that ones found in natural stones. These fingerprint like
inclusions are made up of flux, they tend to stand out in high relief of a white
or yellow color but can sometimes be colorless. A flux fingerprint will usually
be coarser and less elaborate then a natural fingerprint.
Nailhead Spicule: This
type of inclusion resembles a rod like shape with a pointed end resembling the
head of a nail. In a synthetic stone there will usually be more then one found
and they will all point in the same direction. Nailhead spicules are commonly
found in hydrothermal grown synthetic Emeralds.
Chevron Growth: Growth patterns found in hydrothermal type
synthetic stones can display a “V” shaped pattern that is referred to as
Chevron Growth. This inclusion tends to be found in a repeated pattern
of chevron shape growth that all point in the same direction.
Wispy Veil: This
type of inclusion tends to stand out in high relief and have a ribbon like wispy veil
shape to them. Wispy veil inclusions are commonly seen in flux grown synthetic Emeralds.
Columnar Structure: Columnar structure is a unique feature found in synthetic opal. When viewed
under magnification in a profile angle it will appear as spherical columns, and
when viewed from the top in a bird’s eye angle it will appear in a snakeskin
When separating natural diamond
from its many simulants it will require close attention to details beyond
inclusions. Not all man made synthetic diamonds will contain inclusions like
the metallic inclusions found in flux grown, yet there is still ways to separate
them without just the use of magnification. Body color, growth structure,
fluorescence, heft, fire, and pavilion flash are the most helpful indications
for separating genuine from synthetic diamond; also the aide of a diamond tester
is strongly recommended.
Common Characteristics and
Inclusions found in Imitations:
Orange Peel Effect:
The orange peel effect refers to the surface having an uneven and pitted
appearing surface, commonly seen on the reflected surface of glass and
Swirl Marks / Flow Lines:
Swirl marks also referred to as flow lines come from when an imitation stone is
being made and the ingredients have not been mixed enough. They look similar to
curved striae but will usually appear more coarse and less regular then the
appearance of a synthetics curved color banding.
Gas Bubbles: Gas
bubbles are commonly found in glass imitation stones. They take on a
more rounded and larger shape then the ones found in genuine and synthetic
stones. When a gas bubble is found near an edge or tip of a swirl mark
it would be a large indicator that the stone is an imitation. When gas
bubbles form in large groups within one area of the stone it can easily be
mistaken for a fingerprint inclusion, so make sure to look closely at the
size and shape of the inclusion.
Tooth Test: When
separating a genuine cultured pearl from an imitation there is a test called the
“tooth test” that is very helpful. Usually when a genuine cultured pearl is
rubbed across the front edge of teeth it will have a gritty feel, an imitation
will feel smooth.
Heft: We can use our
own personal judgment of how heavy a stone feels in our hand, by doing this
we are judging its heft. Plastic imitations will tend to feel much
lighter in comparison to their natural counterparts.
Whether you’re a small
collector or small business, you can benefit and be more confident in buying or
selling gemstones by building your knowledge of gemstone identification. This
is especially important right now, because spending is down in nearly every
industry and competition for business is at a *premium*. The knowledge and tools
to identify gemstones and synthetics is the backbone of a successful gem
business and the ability to quickly make decisions based on the best information
is critical. You can become a well-known expert within your industry, by
exercising the power of knowledge and hard work. When you have that kind of
status, it becomes easy to get appointments and close sales. HAPPINESS is what
you will feel when you achieve your goal. The credentials used for Gemologist (G.G)
are created by the Gemological Institution of
America where you can find more information on gemstone identification.
hope that this guide will be of help to you in your needs of identifying and
separating gemstones. If you have any comments or questions about the tools used
to aid in gem identification, please contact me via email.
Abbey Zwach, G.G.
Esslinger and Company