Diamond Terminology & Definitions
A
| B
| C
| D
| E
| F
| G
| H
| I
| J | K | L
| M
| N
| O
| P
| Q | R
| S
| T
| U | V | W | X | Y | Z |
American Gem Society (AGS): An educational
institution for gemological studies. Click Here for more information about the American Gem Society (AGS). The AGS Labs were created primarily to
develop and promote universally-accepted standards for grading cut, including
Ideal Cut. For more information on the Ideal Cut, please see our detailed
discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Blemish: A clarity
characteristic that occurs on the surface of a diamond. Though some blemishes
are inherent to the original rough diamond, most are the result of the
environment the diamond has encountered since it was unearthed. For more
information on clarity characteristics, including blemishes, please see our
detailed discussion, Diamond Clarity Articles and The Four C's of Purchasing a Diamond.
Brilliance: The brightness that seems to come from the very
heart of a diamond. It is the effect that makes diamonds unique among all other
gemstones. While other gemstones also display brilliance, none have the power to
equal the extent of diamond's light-reflecting power. Brilliance is created
primarily when light enters through the table, reaches the pavilion facets, and
is then reflected back out through the table, where the light is most visible to
your eye. For more information on brilliance, please see our detailed
discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Brilliant Cut: One of three styles of faceting arrangements.
In this type of arrangement, all facets appear to radiate out from the center of
the diamond toward its outer edges. It is called a brilliant cut because it
designed to maximize brilliance. Round diamonds, ovals, radiants, princesses,
hearts, marquises, and pears all fall within this category of cut. Other styles
of faceting arrangements include the step cut (in which facets are arranged in
concentric rows around the table and the culet) and the mixed cut (in which
either the crown or pavilion of a diamond is cut as a brilliant cut, and the
other part of the diamond is cut as a step cut). Note: Some jewelers use the
term "Brilliant cut" as a synonym for "round diamond." For more information on
the most common shapes of diamonds, please see our discussion
on Diamond Shape Articles and The Four C's of Purchasing a Diamond.
Carat: : The unit of
weight by which a diamond is measured. One carat equals 200 milligrams, or 0.2
grams. The word comes from the carob bean, whose consistent weight was used in
times past to measure gemstones. For more information on carat weight, please
see our detailed discussion, Diamond Carat.
Carbon Spots: An inaccurate term used by some people in the
jewelry industry to describe the appearance of certain inclusions in a diamond.
The term refers to included crystals that have a dark appearance, rather than a
white or transparent appearance, when viewed under a microscope. In most cases,
these dark inclusions are not visible to the naked eye, and do not affect the
brilliance of the diamond. For more information on clarity characteristics,
please see our detailed discussion, Diamond Clarity Articles and The Four C's of Purchasing a Diamond.
Cleavage: The propensity of crystalline minerals, such as
diamond, to split in one or more directions either along or parallel to certain
planes, when struck by a blow. Cleavage is one of the two methods used by
diamond cutters to split rough diamond crystals in preparation for the cutting
process (sawing is the other method). For more information on how a rough
crystal becomes a polished diamond, please see our detailed discussion, From Diamond Mining To The Marketplace Articles and The Four C's of Purchasing a Diamond.
Clouds: A grouping of a number of extremely tiny inclusions
that are too small to be distinguishable from one another, even under
magnification. The result is that, under a microscope, this grouping often looks
like a soft transparent cloud inside the diamond. Of course, clouds cannot be
seen with the naked eye. Usually, this sort of inclusion does not significantly
impact a diamond's clarity grade. For more information on clarity
characteristics, including clouds, please see our detailed discussion, Diamond Clarity Articles and The Four C's of Purchasing a Diamond.
Color Grading: A system of grading diamond colors based on
their colorlessness (for white diamonds) or their spectral hue, depth of color
and purity of color (for fancy color diamonds). For white diamonds, GIA and AGS
use a grading system which runs from D (totally colorless) to Z (light yellow).
For more information, please see our detailed discussion, Diamond Color Articles and The Four C's of Purchasing a Diamond.
Crown: : The upper portion of a cut gemstone, which lies
above the girdle. The crown consists of a table facet surrounded by either star
and bezel facets (on round diamonds and most fancy cuts) or concentric rows of
facets reaching from the table to the girdle (on emerald cuts and other step
cuts). For more information on the parts of a diamond, please see our detailed
discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Crown angle: The angle at which a diamond's bezel facets
(or, on emerald cuts, the row of concentric facets) intersect the girdle plane.
This gentle slope of the facets that surround the table is what helps to create
the dispersion, or fire, in a diamond. White light entering at the different
angles in broken up into its spectral hues, creating a beautiful play of color
inside the diamond. The crown angle also helps to enhance the brilliance of a
diamond. For more information on how crown angles affect a diamond's beauty,
please see our detailed discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Culet: A tiny flat facet that diamond
cutters sometimes add at the bottom of a diamond's pavilion. Its purpose is to
protect the tip of the pavilion from being chipped or damaged. Once a diamond is
set in jewelry, though, the setting itself generally provides the pavilion with
sufficient protection from impact or wear. Large or extremely large culets were
common in diamonds cut in the early part of this century, such as the Old
European or Old Mine Cut. However, such large culets are rarely seen today. Most
modern shapes have either no culet at all, or a small or very small culet. For
more information on the parts of a diamond, please see our detailed discussion,
Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Cut: This refers both to the proportions and the finish of a
polished diamond. As one of "the Four Cs" of diamond value, it is the only
man-made contribution to a diamond's beauty and value. For more information,
please see our detailed discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Depth:The height of a
diamond from the culet to the table. The depth is measured in millimeters. For
more information on the parts of a diamond, please see our detailed discussion,
Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Depth Percentage: On a diamond grading report, you will see
two different measurements of the diamond's depththe actual depth in
millimeters (under "measurements" at the top of the report) and the depth
percentage, which expresses how deep the diamond is in comparison to how wide it
is. This depth percentage of a diamond is important to its brilliance and value,
but it only tells part of the story. Where that depth lies is equally important
to the diamond's beauty; specifically, the pavilion should be just deep enough
to allow light to bounce around inside the diamond and be reflected out to the
eye at the proper angle. Keep in mind, also, that a depth percentage that might
be excessive for one diamond cut might be necessary for another type of cut. For
example, a 75% or 78% depth in a princess cut diamond would be typical and quite
attractive. However, a depth of even 65% would be unnecessary and even
detrimental to a round diamond's beauty. For more information, please see our
detailed discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Diamond: A crystal made up of 99.95% pure carbon atoms
arranged in an isometric, or cubic, crystal arrangement. It is this unique
arrangement of the carbon atoms that makes diamond look and behave differently
from other pure carbon minerals such as graphite (the soft black material used
to make pencils).
Diamond Cutting: The method by which a rough diamond that
has been mined from the earth is shaped into a finished, faceted stone. As a
first step, cleaving or sawing is often used to separate the rough into smaller,
more workable pieces that will each eventually become an individual polished
gem. Next, bruting grinds away the edges, providing the outline shape (for
example, heart, oval or round) for the gem. Faceting is done in two steps:
during blocking, the table, culet, bezel and pavilion main facets are cut;
afterward, the star, upper girdle and lower girdle facets are added. Once the
fully faceted diamond has been inspected and improved, it is boiled in
hydrochloric and sulfuric acids to remove dust and oil. The diamond is then
considered a finished, polished gem. For more information on how a rough crystal
becomes a polished diamond, please see our detailed discussion, From Diamond Mining To The Marketplace Articles and The Four C's of Purchasing a Diamond.
Diamond Gauge: An instrument that is used to measure a
diamond's length, width and depth in millimeters.
Dispersion:The play of small flashes of color across the
surface of the diamond as it is tilted. Dispersion is sometimes also called
"fire." Dispersion is caused when light hits the small, angled facets (bezel and
star facets) arranged around the crown of the diamond; these varying angles
cause the white light to separate into its component spectral colors (for
example, red, blue and green). This play of color should not be confused with a
diamond's natural body color (normally white, though sometimes yellow, brown,
pink or blue in the case of fancy color diamonds) which is uniform throughout
the entire diamond and is constant, regardless of whether it is being tilted or
not. For more information on how light interacts with a diamond, please see our
detailed discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Emerald Cut: A square
or rectangular-shaped diamond with cut corners. On the crown, there are three
concentric rows of facets arranged around the table and, on the pavilion, there
are three concentric rows arranged around the culet. This type of cut is also
known as a Step Cut because its broad, flat planes resemble stair steps. For
more information on the most common shapes of diamonds, please see our
discussion on Diamond Shape Articles and The Four C's of Purchasing a Diamond.
Eye-Clean: A term used in the jewelry industry to describe a
diamond with no blemishes or inclusions that are visible to the naked eye (i.e.
a human eye which is not aided by magnifying devices such as a jeweler's loupe
or a microscope).
Facet: The smooth, flat faces on the surface of
a diamond. They allow light to both enter a diamond and reflect off its surface
at different angles, creating the wonderful play of color and light for which
diamonds are famous. The table below shows all the facets on a round brilliant
cut diamond. A round brilliant has 58 facets (or 57 if there is no culet). The
shape, quantity, and arrangement of these facets will differ slightly among
other Diamond Shape Articles and The Four C's of Purchasing a Diamond.
Fancy Shape: Any diamond shape other than round. For more
information on the most common shapes of diamonds, please see our discussion on Diamond Shape Articles and The Four C's of Purchasing a Diamond.
Feathers: These are small fractures in a diamond. They are
usually caused by the tremendous stress that the diamond suffered while it was
growing underground. In some cases the feather both begins and ends within the
diamond's surface and, in other cases, the feather begins inside the diamond and
extends to the surface. When viewed under magnification, some feathers are
transparent and others have a light white appearance to them. The term "feather"
comes from the fact that, under magnification, these fractures often seem to
have an indistinct, feathery shape to them. While the idea of buying a diamond
with "fractures" may sound scary, the reality is that, with normal wear and
care, most feathers pose no risk to the diamond's stability. Consider this: even
with the feathers, these diamonds survived their growth and their journey to the
surface intact. Once on the surface, they also survived the mining process, as
well as the brutal stresses of the diamond cutting process. Though diamonds are
certainly not invulnerable to damage, basic consideration to their care and
handling during everyday wear will most likely protect them over the course of
several human lifetimes. For more information on feathers and other types of
inclusions, see our discussion, Diamond Clarity Articles and The Four C's of Purchasing a Diamond.
Finish: This term refers to the qualities imparted to a
diamond by the skill of the diamond cutter. The term "finish" covers every
aspect of a diamond's appearance that is not a result of the diamond's inherent
nature when it comes out of the ground. The execution of the diamond's design,
the precision of its cutting details, and the quality of its polish are all a
consideration when a gemologist is grading finish. If you examine a diamond's
grading report, you will see its finish graded according to two separate
categories: polish and symmetry. For more information on finish affects a
diamond's appearance, please see our discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Fire: Please see our definition of Dispersion,
above.
Fluorescence: An effect that is seen in some gem-quality
diamonds when they are exposed to long-wave ultraviolet light (such as the
lighting frequently seen in dance clubs). Under most lighting conditions, this
fluorescence is not detectable to the eye. However, if a diamond is naturally
fluorescent, it will emit a soft colored glow when held under an ultraviolet
lamp or "black light." Fluorescence is not dangerous to the diamond or to the
wearer; it is a unique and fascinating quality that occurs naturally in a number
of gems and minerals. For additional information on the nature of fluorescence
and its effect on diamonds, please see our detailed discussion, Diamond Fluorescence Articles and The Four C's of Purchasing a Diamond.
Gemological Institute of
America (GIA): Founded in 1931 by Roger Shipley, this non-profit
organization upholds the highest standards for grading diamonds and other
precious gems. The GIA has one of the most-respected and well-regarded
gemological laboratories in the world; GIA was responsible for developing and
standardizing the diamond grading system that is used today by nearly all other
gem labs. Click Here for more information about the Gemological Institute of America (GIA).
Girdle: : The outer edge, or outline, of
the diamond's shape. The girdle is not graded, but rather it is described by its
appearance at its thinnest and thickest points. The descriptions of girdle
thickness range as follows: extremely thin; very thin; thin; medium; slightly
thick; thick; very thick; extremely thick. While it is less desirable for a
round diamond to display an extremely thin or extremely thick girdle, such
girdle widths are more common and acceptable in Diamond Shape Articles and The Four C's of Purchasing a Diamond. For example,
shapes such as pears, marquises or hearts may be cut with extremely thick
girdles at their points (and at the cleft, in the case of a heart) in order to
protect these delicates corners from damage. Girdles may be either smooth
(shaped but not polished), polished (a more shiny version of the smooth girdle),
or faceted (tiny little facets running vertically around the entire perimeter of
the girdle). The difference between these types of girdle finishes is generally
not distinguishable to the eye. A polished or faceted girdle doesn't improve a
diamond's grade. For more information on the parts of a diamond, please see our
detailed discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Heart: A type of
fancy diamond cut, which is cut to resemble the popular Valentine's Day shape.
For more information on the most common shapes of diamonds, please see our
discussion on Diamond Shape Articles and The Four C's of Purchasing a Diamond.
Inclusion: A clarity
characteristic found within a diamond. Most inclusions were created when the gem
first formed in the earth.For more information on clarity characteristics,
including inclusions, please see our detailed discussion, Diamond Clarity Articles and The Four C's of Purchasing a Diamond.
Laser-Drill Holes:
One of the few man-made inclusions that can occur inside a diamond. Why on earth
would anyone want to drill holes into a perfectly good diamond? It may seem
counter-intuitive, but drilling this type of hole into a diamond can actually
raise its clarity grade. In some diamonds, the clarity grade may be determined
mainly by the presence of just one or two dark included crystals in a diamond
that is otherwise relatively free of inclusions. In certain circumstances, the
diamond cutter will decide to use a procedure to remove the dark inclusions and,
hopefully, increase the clarity of the diamond. First, a hole is precisely made
with state-of-the-art equipment; it extends no further than it needs to, and its
width is so small (about the size of a pinpoint) that a loupe or microscope is
usually required to detect it. Next, a strong acid solution is forced into the
new hole; since diamonds are resistant to acids, the solution actually dissolves
the included crystal while leaving the diamond completely unharmed. The end
result is a more transparent diamond. The structural stability of the diamond is
not compromised in any way by this hole, and the process is permanent. For more
information on clarity characteristics, please see our detailed discussion, Diamond Clarity Articles and The Four C's of Purchasing a Diamond.
Length-to-width ratio: A comparison of how much longer a
diamond is than it is wide. It is used to analyze the outline of Diamond Shape Articles and The Four C's of Purchasing a Diamond
only; it is never applied to round diamonds. There's really no such thing as an
'ideal' ratio; it's simply a matter of personal aesthetic preferences. For
example, some people prefer the look of a long, slender marquise and others
prefer the look of a shorter, fatter marquise. And while many people like square
princess cuts and radiant, there are some people who enjoy more rectangular
proportions for these types of Diamond Shape Articles and The Four C's of Purchasing a Diamond.
In the ratio, width is always represented by the value "1." To determine the
value of the length, divide the millimeter measurement of the length by the
millimeter measurement of the width. These millimeter measurements can be found
at the top left-hand side of the diamond grading report. The measurements are
always listed in the following order: Length x Width x Depth.
Here is an example of how the length-to-width ratio would be used:
- Consider a princess cut weighing 1.05 carats that has millimeter
measurements of 5.73 x 5.52 x 4.11.
- The first value represents the diamond's length and the second value
represents its width. To calculate the length-to-width ratio, divide 5.73 by
5.52.
- The result is 1.04 and it represents the length as it compares to the
diamond's width (which you will remember is always represented by the value
"1"). This means the length-to-width ratio for this diamond is 1.04 to 1,
which is an almost perfectly square diamond. This diamond will appear square
to your eye.
Marquise Cut: A type
of fancy shape diamond which is elongated with points at each end. For more
information on the most common shapes of diamonds, please see our discussion on Diamond Shape Articles and The Four C's of Purchasing a Diamond.
Naturals: Small parts
of the original rough diamond's surface which are left on the polished diamond,
frequently on or near the girdle. While these are blemishes, they might also be
regarded as a sign of skilled cutting; the presence of a natural reflects the
cutter's ability to design a beautiful polished gem while still retaining as
much of the original crystal's weight as possible. In many cases, naturals do
not affect the clarity grade. In most cases, they are undetectable to the naked
eye. Another type of natural is the Indented Natural; in this
case, the portion of the original rough diamond's surface which is left on the
polished diamond dips slightly inward, creating an indentation. Usually, the
cutter makes an effort to cut the polished diamond so that the indented natural
will be confined to either the girdle or the pavilion (making it undetectable to
the naked eye in the face-up position). For more information on clarity
characteristics, please see our detailed discussion, Diamond Clarity Articles and The Four C's of Purchasing a Diamond.
Oval: A type of fancy
shape diamond which is essentially an elongated version of a round cut. For more
information on the most common shapes of diamonds, please see our discussion on Diamond Shape Articles and The Four C's of Purchasing a Diamond.
Pavé: A style of
jewelry setting in which numerous small diamonds are mounted close together to
create a glistening diamond crust that covers the whole piece of jewelry and
obscures the metal under it.
Pavilion: The lower portion of the diamond, below the
girdle. For more information on the parts of a diamond, please see our detailed
discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Pear: A type of fancy shape diamond that resembles a
teardrop. For more information on the most common shapes of diamonds, please see
our discussion on Diamond Shape Articles and The Four C's of Purchasing a Diamond.
Point: : A unit of measurement used to describe the weight
of diamonds. One point is equivalent to one-hundredth of a carat. For more
information on carat weight, please see our detailed discussion, Diamond Carat.
Polish: Refers to any blemishes on the surface of the
diamond which are not significant enough to affect the clarity grade of the
diamond. Examples of blemishes that might be considered as 'polish'
characteristics are faint polishing lines and small surface nicks or scratches.
Polish is regarded as an indicator of the quality of as diamond's cut; it is
graded as either Ideal, Excellent, Very Good, Good, Fair or Poor. For more
information on other aspects of a diamond's cut, please see our detailed
discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Princess: : A type of brilliant cut fancy shape that can be
either square or rectangular. For more information on the most common shapes of
diamonds, please see our discussion on Diamond Shape Articles and The Four C's of Purchasing a Diamond.
Radiant: A type of
brilliant cut fancy shape that resembles a square or rectangle with the corners
cut off. For more information on the most common shapes of diamonds, please see
our discussion on Diamond Shape Articles and The Four C's of Purchasing a Diamond.
Ratio: Please see our definition of Length-to-Width Ratio,
above.
Semi-mount: A jewelry
setting that has the side stones already mounted, but which contains an empty
set of prongs which are intended to mount a diamond center stone that the
customer selects separately.
Single-cut: A very small round diamond with only 16 or 17
facets, instead of the normal 57 or 58 facets of a full-cut round brilliant.
Single cuts are occasionally used for pavé jewelry and other jewelry that
utilizes numerous small diamonds set closely together. For more information on
the most common shapes of diamonds, please see our discussion
on Diamond Shape Articles and The Four C's of Purchasing a Diamond.
Step Cut: One of three styles of faceting arrangements. In
this type of arrangement (named because its broad, flat planes resemble stair
steps), there are three concentric rows of facets arranged around the table and,
on the pavilion, there are three concentric rows arranged around the culet.
Other styles of faceting arrangements include the brilliant cut (in which all
facets radiate out from the center of the diamond toward its outer edges) and
the mixed cut (in which either the crown or pavilion of a diamond is cut as a
brilliant cut, and the other part of the diamond is cut as a step cut). For more
information on the most common shapes of diamonds, please see our discussion on Diamond Shape Articles and The Four C's of Purchasing a Diamond.
Symmetry: : Refers to variations in the symmetry of a
diamond's arrangement of facets. The small variations can include misalignment
of facets or facets that fail to point correctly to the girdle (this
misalignment is completely undetectable to the naked eye). Symmetry is regarded
as an indicator of the quality of as diamond's cut; it is graded as either
Ideal, Excellent, Very Good, Good, Fair or Poor. For more information on other
aspects of a diamond's cut, please see our detailed discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Table: The flat facet on the top of the diamond.
It is the largest facet on a cut diamond. For more information on the parts of a
diamond, please see our detailed discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Table percentage: The value which represents how the
diameter of the table facet compares to the diameter of the entire diamond. So,
a diamond with a 60% table has a table which is 60% as wide as the diamond's
outline. For a round diamond, gemologists calculate table percentage by dividing
the diameter of the table, which is measured in millimeters (this millimeter
measurement does not appear on diamond grading reports) by the average girdle
diameter (an average of the first two millimeter measurements on the top
left-hand side of a diamond grading report). For a fancy shape diamond, table
percentage is calculated by dividing the width of the table, at the widest part
of the diamond, by the millimeter width of the entire stone (this total width
measurement is the second of the three millimeter values in the top left-hand
corner of the diamond grading report. Contrary to popular misconception, having
a small table percentage (53% to 57%) does not make a round diamond any more
brilliant than a diamond with a larger table. For more information, please see
our discussion, Diamond Cut Articles and The Four C's of Purchasing a Diamond.
Trilliant: A type of brilliant fancy shape that is
triangular. For more information on the most common shapes of diamonds, please
see our discussion on Diamond Shape Articles and The Four C's of Purchasing a Diamond.
