The doubled facet reflections seen under magnification in this
sphene and zircon, serve as clues to gem identity : few species
have birefringence this high
Is it natural
or synthetic? Once the question of the species or variety has been answered,
then it is necessary to know whether the gem is natural or synthetic.
(Remember, synthetics are the gem, and, therefore, have all the chemical,
physical and optical properties of the natural version). One of the
best tools at a gemologist's disposal, in trying to make this call,
are certain inclusions found only in natural stones, and others found
only in synthetics. In many cases, then, seeing a certain inclusion
is definitive. Unfortunately, there are also inclusions which can be
found in either type, and some gems that are so totally clean, there
are no inclusions to use.
triangular platinum Crystals which were eroded from the crucible
in which this synthetic Alexandrite was formed, give proof of
its man-made origin
it been enhanced, and if so, how? Certain enhancements (and imitations)
can be most easily detected by a magnified view of the surface, or the
interior, of a gem.
The intact "silk" (rutile needles) in this sapphire
proves that it has not been subjected to high heat, and is of
natural color, whereas the stress fractures in this heated sapphire
give evidence of its treated state
specifically, did it come from? Though not a factor in most cases, there
are a few important instances where the geographic location of a gem's
origin is crucial in setting its value. In those situations, it is often
possible by seeing diagnostic inclusions or growth features to specify
the location. Only peridot from Arizona shows a characteristic stress
fracture/included crystal combination known as a "lily pad",
and only demantoid garnet from Russia, shows microscopic curving fibers
of bryssolite asbestos known as a "horsetail".
pads in Arizona Peridot
horsetail inclusion in Russian Demantoid Garnet
You can see very cool things :
Looking into a gem can reveal a world of beauty and complexity that
just isn't apparent from a surface view.
two tools most often employed in gemstone magnification are the loupe
and the gem microscope.
loupe: A loupe is a small magnifying device, which, most commonly, magnifies
the object to be viewed to ten times its size (10x). There are five
major types used by those observing gems: handheld, eye socket, headpiece,
eyeglass, and darkfield. Each has its advantages and particular best
use. The handheld version is the most versatile, and the darkfield type
supplies a source of specialized lighting important in some aspects
of gem identification and/or grading. The eyesocket, headpiece and eyeglass
types have the advantage in situations where leaving the hands free
general, the advantage of a loupe over a microscope is its portability
and low cost. On the other hand, the loupe's capabilities of magnification
and lighting are limited compared to most microscopes.
Some of you probably already own a loupe or have taken the advice from
the course syllabus and recently acquired one. So, before we get any
further into the technical aspects of magnifying tools and techniques,
let me give a warning: Use this tool with caution the view can be scary
sometimes! The first time a new loupe-user looks at their favorite piece
of gemstone jewelry at 10x, they are in for for a rude awakening.
A piece of gemstone jewelry which has been worn to any extent (and which
looks perfectly fine to the naked eye) shows, to the examiner with a
loupe, scratches and gouges in the metal, and glaring manufacturing
flaws like incomplete solder joints. Upon turning his/her attention
to the gem, what meets the eye is globs of dirt and grime surrounding
the gem, and in most cases startlingly visible "crud" inside
the gem, and/or worrisome chips, scratches or fractures on its surface.
By way of demonstration, let's look at a couple of perfectly lovely
gemstones: a (rather expensive) Tsavorite garnet, and a modestly priced
bicolored tourmaline cabochon.
Tsavorite gem has no visible problems and looks great, completely transparent
and full of sparkle and color. The tourmaline, as is the case with most
cabochon gems, is of lower quality than a piece that would have been
faceted, and is translucent, but still very attractive.
view using our loupe, is somewhat different :
OK, now that I've properly warned you, let's look
on the bright side and view some of the "very cool" things
for fun :
a nice dendritic chalcedony which at 10x really shows the three dimensional
nature of the dendrites and gives some insight into their growth pattern
drusy gems, but at 10x we can actually tell that their surfaces are
lined with real crystals (albeit small).
quartz at 10 X
of pictures below is of the same inclusion within a gem the gem has
been tilted about 30 degrees in the second shot. What you are seeing
is the movement of a gas bubble within a pool of liquid within a cavity
in the gem. The first time you look inside a rock and see something
moving it's quite a thrill! Such a moveable bubble is referred to as
an "enhydro" and is much sought after by collectors.
"enhydro" inclusion in Quartz
Hand Loupe :-
The highest quality (and most expensive) loupes actually consist of
a set of three glass lenses fitted together, and are referred to as
"triplets". Together, the set of lenses corrects for the inevitable
distortion introduced when a single lens is used.
This distortion is of two types: chromatic
and spherical, and both types are caused by the curved shape of the
lens, particularly at the edges where the curvature is the greatest.
In chromatic distortion, the unequal bending of the different color
wavelengths creates dispersive color fringes at the edges of view. In
spherical distortion, a similar mechanism causes the image itself to
curve and be out of focus in those areas.
Single lens loupes are available at very low cost, and are just fine
for non-professional applications. If your loupe is not a triplet type,
no need to worry all you need to do to compensate, is to confine your
observations to the central area under view, and things will be fine.
Hand loupes can be found from 2x to
30x magnification. It might seem a good choice to purchase the one with
the highest power, but typically that is not the case. There are three
1. The higher the power of magnification, the shorter the "focal
length" the distance from the lens to the object so that it is
in focus. For a 10x lens that distance is one inch, (20x = 1/2 inch,
and 30x = 1/3 inch). It is difficult enough to work with a 1" clearance,
let alone any of those shorter distances!
2. The shorter the focal length (higher power) the less light can enter
the gem. Again, getting proper lighting at a distance of 1" can
be a challenge, but it is very much more difficult at the shorter distances
available at higher magnifications.
3. The higher the power of magnification, the smaller the "focal
area" the size of the patch that you are magnifying. It can take
quite a while to throughly examine all areas of a gem while using 10x,
the job becomes harder, the smaller the "patches" you are
It should not be surprising then, that
the vast majority of loupes in use are 10x.
loupes come with a metal cover that doubles as a "finger hold"
or handle. The correct technique for using a loupe is pictured and described
Put the index finger of your non-preferred hand (left hand for righties,
and vice versa) through the loupe cover and bring the loupe to rest
against your thumb which is resting on your cheekbone. (This gives you
just about the right eye-to-loupe distance.
2. In your other hand are your tweezers with the stone (either a girdle
to girdle, or a table to culet hold is fine). The tips of the tweezers
are between your middle and fourth finger. This allows you to easily
and stably pivot the stone forward and back (with the hand holding the
tweezers) to adjust the focal length to the 1" required.
3. Once you have mastered the basic "hold" you can actually
focus on different "depths" within the gem by slightly increasing
or decreasing the gem's distance from the loupe. First bringing the
surface into focus, for example, then moving the focal area into the
interior and finally to the bottom of the gem.
4. Unless you have severe astigmatism you do not need to wear your glasses.
5. Keep both eyes open. If you haven't used magnifying devices before,
this takes some discipline to do, as your natural inclination is to
close one eye. You can view comfortably for a much longer period of
time with the "two eye" technique, and as a bonus, you usually
don't end up with a headache.
Darkfield Loupe :-
The ideal lighting condition for revealing
inclusions in a gem is known as: "darkfield illumination".
In this situation the gem is viewed against a black background with
the light coming through it only from the side. The effect is to make
any interior features stand out sharply in relief, and to be much more
noticeable than with ordinary lighting. Although gem microscopes provide
this lighting choice, most loupes do not. The exception is a device
known as a darkfield loupe. The housing into which the gem is placed
for viewing has a central, black baffle which prevents light from the
source (usually a small "maglite" type of flashlight) from
shining straight into the gem. Instead the light is reflected from the
shiny sides of the housing to enter the gem sideways.
The technique for using a darkfield
loupe, couldn't be simpler: the gem, in its tweezers, is simply rested
in the opening and viewed at a comfortable distance. These are much
more expensive than hand loupes, but for those who need to grade gem
clarity on a regular basis, are well worth it.
A gem microscope is similar to a biological
or medical microscope in that it is binocular, and uses compound lenses.
A binocular magnifying device has two eyepieces so that both eyes are
used at once. This is ideal for getting a good three dimensional view.
In a compound scope, there is a set of lenses close to the object being
magnified (objective lenses) and a set in the eyepieces (ocular lenses).
With this set-up, magnification is compounded, meaning that, for example,
if the objective lens is 5x and the ocular lens is 10x, the total magnification
Gem scopes differ from biological scopes
in that the total maximum magnification is usually lower (about 70x
as compared to as much as 1000x) and there are more lighting options.
For example, a good gem microscope has: brightfield illumination, darkfield
illumination, oblique lighting, overhead lighting, a light diffusing
system, a system for immersing the object in liquid in a well for viewing,
and a light polarizing set up. They also generally come fitted with
a pivoting stone holder.
typical gemological microscope
eyes open is best
In the diagrams of the under stage areas
of the microscopes below, you can see a comparison of brightfield and
With brightfield lighting the light
entering the gem comes from below as well as from the side. The amount
of light entering the viewing area is manually controlled by an iris
diaphragm, and frequently diffused with a special frosted glass coverplate.
This type of lighting is ideal for seeing color zoning, dye concentrations,
and the curved growth bands indicative of certain types of synthetic
important is overhead lighting (sometimes called reflected or incident
lighting). In this case the light source in the well of the microscope
is turned off, and an overhead light used instead. Such illumination
is excellent for examining the surface of the gem for blemishes, and
for details of the finish, such as polish and facet meets.
the two pictures below taken of the same gem (at 10x magnification)
under reflected light and darkfield. Notice how the surface features
are so much more noticeable in the first instance, and the internal
features better displayed in the second.
Can Be Seen? :
clarity characteristics of a gemstone are divided into those that are
seen on the surface (blemishes) and those in the interior (inclusions).
Blemishes and other surface features: In this category are chips, scratches,
knicks and abrasions, as well as attributes of the faceting or lapidary
process such as degree of polish, or shape and placement of facets.
A survey of the outside of the gem can yield several important results.
1. Gems are graded for color, clarity and cut. Some of the surface features
are used in setting the gem's clarity and/or cut grades. Surface features,
in general, affect the clarity grade less than do inclusions, but there
are some important exceptions. A surface-reaching fracture, for example,
is considered a blemish, but it greatly diminishes a gem's clarity grade
because it decreases durability.
2. The surface view can yield important gem identification information.
Examples would be abraded facet junctions which give hardness clues,
or characteristic surface features like the "engine-turned"
effect that is diagnostic for elephantine ivories.
3. Telltale signs of imitation gems or gem enhancement are often observable
on a gem's surface. This would include concave facets or mold marks
as seen on glass and plastic, and dye concentrations in surface reaching
are some examples of important surface features :
and other internal features :-
Internal clarity characteristics of a gemstone are represented by four
major groups: solids, cavities, cracks and growth phenomena.
1. Solids :
Solid material seen inside a gem is usually some type of included crystal.
Crystals can be large or small, they
can have an RI similar to, or quite different from, their host, and
they can be many different species, including the same species as the
Not only are the crystals likely to
affect the clarity grade of the gem, they also can be suggestive or
diagnostic of its species, enhancement status, or location of origin.
Included crystals with rounded, rather than sharp edges, can be indicative
of high temperature heating for example which might occur naturally
or during certain types of treatments.
The majority of crystals are either
formed at the same time as the gem, from other minerals present in the
melt, vapors or fluids, or pre-existing ones which the growing gem captures.
Less frequently, the crystals appear after the gem is first formed.
A noteworthy process, in this regard,
is "exsolution". It occurs after the initial formation of
the gem, and involves re-crystalization of materials which may, initially,
have been dissolved in the gem.
Gems may have several stable points of temperature and pressure at which
they can crystallize. Picture a gem forming at one set of conditions
and then later being partially, or wholly, remelted and subjected to
new conditions. Rutile, for example, can be dissolved in corundum, or
exsolved. When it exsolves it crystallizes as discrete needles. This
phenomenon is used by gem treaters to add or subtract rutile needles
from sapphire at will, respectively ehancing the potential star in a
gem, or clarifying a cloudy one.
Another "after the fact"
way in which crystals get into a gem is by invasion of cracks by fluids.
This is the mechanism by which the dendrites in chalcedony form, as
well as that which is responsible for the seams of precious opal in
a matrix rock.
Crystals in Spinel
Crystal in Diamond
"sheaf" in Citrine
and Prismatic Crystals in Beryl
Fibrous hematite cyrstals in strawberry
Voids within a gem can contain liquid, gas (bubbles) or solids, and
as remnants of the gem formation process, are quite often important
in determining identity or the location of origin. Since bubbles are
extremely rare in natural crystalline gems, they are very good indicators
of either amorphous gems like glass, or synthetics.
usually can be distinguished by their rounded or oblong shapes, and
their very high relief. In cases of doubt as to whether something is
a bubble or a rounded off crystal, polarized light can generally be
used to discriminate.
in Moldavite (a natural glass)
in Cubic Zirconia (a synthetic)
with both a liquid and a gas trapped inside are called "two phase"
inclusions, and those that also contain a solid crystal are termed "three
phase"inclusions. In the vast majority of cases, two and three
phase inclusions are indicative of natural origin.
It's time to learn a new euphemism! Cracks, which can be either fractures
or cleavages, are, in the gem world, given the disarmingly attractive
name of "feathers". It does sound nicer, doesn't it, to say
that your gem has several feathers, rather than using harsher (but more
can occur during the formation of a gemstone, perhaps as a result of
rapid heating or cooling, or through pressure or mechanical stress.
They can also occur long after the formation process, for the same reasons.
They can be entirely within the gem or can reach the surface.
some conditions such a break within a gem can act as a diffraction grating
and create a small dispersive rainbow of color, known as a "cleavage
rainbows in a quartz specimen with an internal fracture
rainbows in a piece of diamond rough with an internal fracture
fractures not only impair durability, they also are portals for fluids
to enter which may cause stains or, in the case of enhancement, accept
and concentrate dyes.
non-surface reaching feather within a Tourmaline
surface reaching crack in a Sapphire showing natural staining
fractures in these Indonesian chalcedonies have allowed iron staining
to create fortuitously meaningful patterns
that exist within a still-forming gem, can be partially healed by penetration
of growth fluids, or later by partial remelting of the material. Such
partially healed cracks often show up under magnification as a series
of tiny dots in rows or arcs. They look quite a bit like their namesake:
natural Ruby containing multiple fingerprints
of fingerprints in Kunzite
of fingerprints in Tsavorite garnet
healing process, in essence, acts like a set of tiny "spot welds"
which hold the sides together, and prevent the crack from enlarging.
For this reason, the presence of fingerprints in a gem does not negatively
affect its durability, and usually, unless there are so many of them
that they impede light, have little effect on the gem's transparency.
knowledgeable observers are happy to see at least a small fingerprint
in a gem, as it is very strong evidence that a gem is natural rather
than synthetic! There are some inclusions in synthetic gems which superficially
look like fingerprints, but close examination by a trained eye can usually
identify them not as fingerprints, but as remnants of the solid fluxes
used in the synthesizing process.
gem ehancement processes exist whereby surface reaching feathers in
a gem can be "filled" with oils, resins or glass. The goal
here is to disquise the crack by replacing the air in it with something
closer to the gem's RI, thereby reducing its relief. This is a standard
practice for emeralds, and occasionally seen in rubies and diamonds.
Similar techiques are in use to fill the cracks caused by "crazing"
in opals. In diamonds, lasers have been used to tunnel inside to reach
internal feathers and treat them.
Oil-filled fractures in Emerald
Growth Phenomena :
This "catch-all" category includes visible evidence of twinning,
and other features of the gem's growth . Examples include "swirl
marks" which occur in amorphous materials, primarily glasses, and
either curved or straight growth or color zoning patterns which may
help distinguish natural from synthetic gems.
single crystal gems, curved growth lines (striae) or color patterns
always mean synthetic, whereas straight ones can be found in either
natural or synthetic gems. Growth and color zones are best observed
with diffused light or under immersion in a liquid.
marks in Moldavite, indicating glass
growth striae proving the synthetic origin of this Ruby
growth zoning in synthetic flux grown Ruby
color zoning in natural Sapphire
columnar or "chickenwire" pattern of color blocks in opal
is a sure sign of a man-made product.
and columnar opal color blocks proving man-made opal
Clarity Grading of Gems :-
reality is that the clarity of gems runs as a continuum from completely
flawless to extremely highly included. Humans, though, always like to
make boundaries and put things into discrete categories, and so it is
with clarity grading of gems. Grading systems, especially for colored
stones vary widely in the exact terminology they use, but all such systems
describe at least four major categories of clarity:
1. Flawless :
No inclusions can be seen, even at 10x magnification. Very few gems
are in this category as the geological and biological processes which
create gems usually leave some visible evidence. Some types of laboratory
synthesis processes routinely produce flawless stones, while others
yield gems with inclusions. (Flawless natural-origin gems come at a
premium price, and it would be prudent for anyone contemplating a high
value purchase of a gem without inclusions, to have the gem certified
as natural by a gemological laboratory, as there will be no visible
internal evidence as to origin.)
2. Eyeclean :
In this category, gems, as seen under the normal viewing conditions:
face up, in normal lighting, and about 12-14 inches from the viewer,
look clean. Increasing the light or turning the gem on its side or bottom
(which cuts down on reflections) may reveal visible inclusions, though.
When viewed at 10x, gems in this category range from having few and
hard to find inclusions, to having large, rather obvious ones. To many,
this is the ideal condition for a gem--> the reason being that there
are internal signs of its natural origin, yet it still looks great.
3. Slightly Included :
Gems given this description, or some variant of it, have eye visible
inclusions or blemishes, but they do not notably spoil the beauty of
the gem, nor markedly degrade its durability. Some types of gem materials
are rarely found with greater clarity than this: examples would be emeralds
and many red and pink tourmalines. Often gems with visible inclusions
are good bargains as they can still look very nice, but are usually
available for lower per carat prices than those of higher clarity.
4. Included :
This category covers the gems with such overtly visible or numerous
inclusions as to moderately to severely impair beauty or durability.
Usually only very rare collector gems, or extremely inexpensive pieces
are acceptable in this condition.
main groupings can be subdivided into a larger number of groups by using
terms and phrases like: "very slightly", "moderately",
"almost", "better than", just short of", etc.,
to modify the main terms. So, for example, a colored gem that has few
and tiny eye visible inclusions might be called "very, very, slightly
included" while one that has only one or two barely findable inclusions
under 10x might be termed "better than eyeclean" or perhaps
"just short of flawless at 10x".
Colored Stones vs Diamonds :-
Colored stones are frequently clarity graded with the naked eye, and
to less exacting standards than are diamonds. GIA, for example, uses
seven categories for colored stone grading, while with diamonds, which
are clarity graded at 10x, eleven different clarity groupings are made.
Within colored stones, the standards for clarity vary by species. Some
types of gems occur commonly with few inclusions, while other types
generally have many. Emeralds are an example of a gem that rarely, if
ever, is found in clarity greater than eyeclean, while amethyst is often
quite clean, even at 10x. Emerald clarity, therefore, is usually graded
on a less rigorous scale than that used for amethyst. The inclusions
that rate a clarity of: slightly included for an emerald, might generate
a grade of "moderately included" for an amethyst.
a species, then, the grade is set, by the overall number, position and
type of inclusions. Those that affect beauty or durability will be the
most important. Examples of inclusions or blemishes which have a minor
impact on grade would be: a group of tiny crystals located under a bezel
facet where reflections make them hard to see, a poorly polished table,
or color zoning which cannot be seen face up. (In general, blemishes
have slight impact on the clarity grade due to the fact that a gem can
be repolished or recut to remove them). Examples of serious inclusions
would be: a surface reaching fracture, especially on the girdle or crown
(where the gem is subject to the greatest stresses), a "reflector
inclusion" (one whose position causes light reflections to create
multiple images of it) or a "stab in the heart" (an inclusion
clearly visible through the table of the gem).
single "reflector" inclusion which appears, by reflection,
to be many, in a Diamond
black "stab in the heart" inclusion visible through
this Sunstone's table. (near center, right)
Exception to the Rules :-
A notable exception to the way in which gems are clarity graded would
be in the case of those gems whose visible inclusions create its value,
rarity, or beauty. In that case, only the surrounding gem material is
clarity graded. In the photos below, we see two such cases: the "trapiche"
emeralds with their black "cog-wheel" inclusions are rare
collectors items, and so the clarity grading would be done in regards
to the green areas only, the "confetti" sunstone is desirable
primarily due to its glittery hematite particles which flash gold, red
and blue, so the clarity grade speaks to only other, extraneous, inclusions
that might be present.