Glossary For Colored
Gemstones and Diamonds
A, B, C,
D, E, F, G,
H, I, K, L,
M, N, O, P,
R, S, T, U,
V, W, X, Y,
- First designed by Marcel Tolkowsky, this type of cut is also called an
Ideal cut. Tolkowsky used mathematics to calculate the proper proportion
to increase a diamond's brilliancy (fire)
when cut in a round shape.
- A gem material which is either a manmade imitation or a synthetic. (See
ASTERISM - The
optical phenomenon of seeing a rayed figure in the form of a star. This
is caused by the reflection of light from minute oriented and aligned needle-like
- Rectangular style of step cut used for small gem materials.
BAROQUE - Irregular
in shape, such as baroque pearls, tumble-polished stones, or freeform shaped
BEAD - A spherical
object, with or without facets, distinguished by a hole drilled through
the stone, usually on center.
BIWA PEARL -
A mantle-tissue, nucleated, freshwater cultured pearl from Lake Biwa, Japan.
Properly called a freshwater pearl.
Any surface imperfection within or on a gemstone. For example, on a diamond,
one would be referring to a nick, knot, scratch, abrasion, minor crack
or fissure (cavity), or a poor polish.
- A diamond with a distinctly blue body
color, even if very light in tone. This type of diamond is considered a
"fancy" diamond. (Note: Diamonds can have blue tonal hues artificially
added such as with color enhanced diamonds).
- A term used for many years that refers to a diamond
without a distinctive body color. It has been used inappropriately to describe
yellow tinted stones. An American Gem Society
ruling prohibits the use of this term by its members. Legally a Blue-White
diamond must have a blue body color. The many flagrant misuses of this
term have rendered it almost meaningless.
Total amount of white light returned to the eye from the gem material as
the result of internal and external reflections. The major factors that
affect the amount of brilliancy in a gem are refractive index, proportions,
polish and transparency.
- The most common style of diamond cutting,
also used for many other popular gemstones, that consists of a round shaped
stone with 57 or 58 facets.
BUBBLE - Any
transparent inclusion in a diamond. It
can also refer to another diamond crystal within a diamond or a grain of
a different material.
- An unfaceted cut stone of domed form (having a convex surface). Often
called a "cab."
CAMEO - A gem
material, usually composed of two or more different colored layers. The
top portion is carved in relief above the girdle plane and the bottom portion
acts as the background for the carving in addition to giving a depth dimension
to the piece. Usually carved in onyx or the traditional material from Italy
which is shell.
CANARY - A term
referring to the intense hue of yellow in a diamond.
Also called "fancy" if the yellow makes the stone very distinctive.
CARAT - A unit
of metric measurement used for gems. One carat (ct.) equals 100 points,
200 milligrams, or 1/5 of a gram.
- Any black appearing inclusions in a diamond
caused by the addition of the minerals graphite or hornblende.
CHANGE OF COLOR (COLOR CHANGE)
- A phenomenon of some colored stones in which the gem material appears
a different color in different types of light. This is caused by selective
absorption and/or transmission of the specific type of light to which the
gemstone is exposed.
The phenomenon of a sharp, well defined band or streak of light across
the dome of a gem material caused by the reflection of light from parallel
CHIP - A term
that has many uses in gemology, it can refer to a small rose-cut or single
cut melee. A cleavage piece of diamond
that weighs less than 1 carat, or a curved break in a diamond.
CLEAN - A trade
term, usually meaning "free from noticeable flaws."
CLEAVAGE - The
tendency of a crystalline mineral to break in certain definite directions
called cleavage planes. The breakage is done by cleaving, a process where
a stone is studied so that the plane may be defined and broken with a swift
blow. This swift blow splits the stone into proportions for fashioning
more economically or for allowing better quality selection.
- Uneven color distribution in a gem material; it appears as bands of varying
colors or different tones or values of the same color. The bands may be
straight, curved or angular in appearance.
- Uneven color distribution in a gem material appearing as irregular patches
of varying colors or different tones of the same color.
- A gemstone of any species other than diamond.
This usage arbitrarily classifies all varieties, but still does not include
colored diamonds. This system has, however, proven to be a practicable
and satisfactory general classification.
CROWN - The part
of any faceted gemstone above the girdle.
CULET - The small
facet polished across what would otherwise be the sharp point or tip of
the pavilion of a faceted stone, especially one of round brilliant cut.
It is cut and placed with the full intention of avoiding breakage of this
CULTURED - A
pearl produced by artificially inducing
the formation of a pearl sac, usually by the introduction of a shell bead
or square mantle tissue into the body of a possible pearl bearing mollusk
(oyster or clam).
CUT - Style or
form (shape) in which a gem material has been fashioned and/or the proportional
- A mineral that is composed of carbon with a hardness of 10 and that is
single refractive. In its transparent form it is the most highly valued
of gemstones. The stones can come in all colors of the rainbow and are
The separation of white light into its component spectral colors (see fire).
DOUBLET - An
assembled stone of two portions bound together by a cement or fused together
by heat. An opal doublet, for example, may be opal cemented to black onyx
with a black colored cement.
A combination of hardness, toughness and stability that describes a specific
- A vitreous glaze. In jewelry, it is usually fused glass that is heated
to a base - most commonly to the surface of metal, glass or pottery.
- One of the small, cut and polished planes that is placed on a gemstone
to increase brilliancy and beauty. It can also occur naturally as approximately
placed planes in the top of a gemstone crystal. This is normal crystal
- A girdle of a stone that is lapped and polished for maximum surface reflection
and has many flat planes around the circumference of the stone.
Any operation employed in preparing rough gem material into polished gemstones
such as cleaving, cutting, or faceting.
FEATHER - A trade
term commonly applied to almost any flaw inside a stone and, more specifically,
to a jagged irregularly shaped fracture which is white in appearance. In
gemology, feather is a term used to describe a series of inclusions which
-- under a microscope -- appear as elongated, irregular in shape and grouped
together in an orderly proximity that resemble the pattern of a feather
on a bird's wing.
FINISH - The
term referring to certain details of fashioning such as the placing and
polishing of the girdle, culet and facets.
FIRE - Flashes
of spectral colors seen in gemstones as a result of dispersion.
FLAW - Any external
or internal imperfection of a diamond
or other transparent gemstone such as an inclusion.
- The process of a material emitting electromagnetic radiation when it
is subjected to radiation. In gemology, the usual influencing radiation
is ultraviolet light and the emitting radiation is visible hued light.
For example, diamonds under ultraviolet light will often emit a visible
light of a blue hue (or other colors).
FOILBACK - Any
gem material that has an applied metallic backing to improve color, brilliance
and/or phenomena such as a glass, rhinestone-accent stone, or other material.
FOUR C'S - A
phrase used to describe a diamond's characteristics,
all starting with the letter "C". The four categories used to
define a diamond's worth are: cut, clarity, color and carat weight.
FRACTURE - A
break or chip in any direction not parallel to the planes of the atoms
in a crystalline mineral and other than on or across cleavage planes. In
other words, any uneven break.
- A pearl that is harvested in a fresh water
FULL CUT DIAMOND
- A description of a brilliant cut, round stone. A diamond
with 57-58 facets.
- A cut and polished material which possesses the beauty, durability and
rarity necessary for use in jewelry. Also used to describe an especially
fine specimen such as a gem emerald.
GEMOLOGY - The
study of gemstones. It includes the study of their identification, grading
and appraisal as well as the examination of their symbols, fashioning,
history and marketing.
GIA - (Gemological
Institute of America) A nonprofit, endowed, educational institute maintained
for the benefit of industry and the public. Many educational courses are
offered for advancement and knowledge within and about the trade.
GIRDLE - The
outer edge, or periphery, of a fashioned stone; the portion that is usually
grasped by the setting or mounting via prongs or bezels. It is the dividing
line between crown (top) and pavilion (bottom) of a gemstone. It can be
ground, bearded, polished or faceted. It can be cut thick or thin, but
is designed to help avoid breakage.
GLASS - An inorganic,
amorphous substance that is in a unique physical state. It cools to a rigid
state, however, without crystallization. A variety of constituents may
be used to create it. The jeweler usually encounters glasses that are mixtures
of silica fused with a variety of other substances that impart various
desirable qualities such as a low melting point, brilliancy and opacity.
Glass is available in many, if not all, colors of the rainbow.
- A gem's ability to resist scratching.
HUE - Any sensation
of color other than black, white or gray (a specific color).
- A general term used to refer to any inclusion, internal or external in
a gemstone -- a feather, carbon spot, knot, fissure, or scratch.
INCLUSION - In
its broadest sense, any optically detectable irregularity in a gem material.
In a narrower sense, any foreign material caught up during the growing
or formation process. Inclusions are usually used to map and identify a
INTAGLIO - A
gem in which the design has been engraved or carved into the stone.
INTENSITY - The
attribute of a color, which determines its position on a scale from vivid
to dull. Traces of brown or gray decrease the intensity of a stone (the
amount of color saturation).
Prismatic colors inside or on the surface of a material caused by light
interference from thin layers of differing refractive indices. These layers
may be thin films of liquid, gas or solid.
- An inclusion that is encountered at the surface of a stone during the
cutting and polishing of a diamond. It
can stand out as a small raised surface on the finished stone.
- Visible with the aid of a loupe (a magnifying eye piece used to examine
a gemstone, usually 10X).
LUSTER - The
appearance of a surface in reflected light.
- Trade term referring to the proportions, symmetry, and polish of a gemstone.
MARQUISE - A
gem shape that is elliptical but with pointed ends, similar to the shape
of the boat.
MELEE - A term
used primarily to describe small, round faceted diamonds
of approximately .18 carat or less. It is also applied to colored stones
in similar sizes as well.
MINERAL - An
inorganic substance with a characteristic chemical composition and a definite
MOHS SCALE -
A loose scale of hardness, used for field collecting, which allows for
identification of specimens. The comparative scale of hardness is as follows:
1) talc, 2) gypsum, 3) calcite, 4) fluorite, 5) apatite, 6) orthoclase,
7) quartz, 8)
topaz and beryl, 9) corundum and 10) diamond.
- Trade term for that portion of a piece of jewelry in which a gem or other
object is to be set or has been set.
- The iridescent substance containing aragonite and calcite crystals. This
is an important outside layering material and a constituent of a pearl
and cultured pearls. The thicker the nacre the longer the pearl has
been allowed to grow. This results in longer durability.
NATURAL - A trade
term for a portion of the original surface of a rough diamond, usually
at the girdle, left by the cutter of a fashioned stone.
- A pearl that originates naturally in a
mollusk, as distinguished from cultured or imitation pearls.
NAVETTE - Usually
considered the same shape as that of a marquise, which is a cut shape where
the girdle is similar to the outline of a boat.
NICK - A minor
chip out of the surface of a diamond,
usually caused by a light blow, found near or on the girdle of the stone
(a percussion mark).
- Milky or pearly appearance of some common opal,
opalescent glass, and other similar substances.
OPAQUE - Transmitting
no apparent light; not transparent.
ORIENT - Minute
prismatic sheen on or just below the surface of a pearl
or cultured pearl caused by the interference and diffraction of light from
the minute crystals comprising the nacre.
OVAL CUT - A
brilliant style of cutting in which the girdle shape is oval or elliptical.
- A style of setting small stones as close together as possible in two
or more rows.
PAVILION - That
portion of a faceted diamond or other
gem material that lies below the girdle.
PEAR SHAPED CUT
- A variation of the brilliant cut with the girdle outline of the stone;
PERFECT - The
Federal Trade Commission considers it
an unfair trade practice to use the word perfect or any other word, expression
or representation of similar derivative, as a description of any diamond
with inclusions that are visible to the naked eye or up to 10X power magnification.
This term has been so flagrantly misused in the sale of diamonds, that
many jewelers avoid its use entirely.
PIT - An indentation
on the surface of a diamond, caused by
a blow, knot or the opening of a cavity during cutting or polishing.
PLAY OF COLOR
- Variety of prismatic colors seen in rapid succession. A phenomenon seen
in opal, fire agate, and other similar stones
caused by the interference and diffraction of light.
POINT - A measurement
in the weight of a diamond equal to 1/100
of a carat. Thus, .50 carats is equal to 50 points.
POLISH - The
smoothness of a surface plane or planes in which optical reflection is
maximized and shows no visible wheel or burn marks.
- A girdle that has been lapped to yield a uniform highly reflective surface
or many surface planes (as in a faceted girdle).
- Returning of light which strikes the surface of a stone.
The change in the velocities and angles of light rays as they pass obliquely
from one medium to another of a different density.
Historically, rock crystal quartz in the jewelry trade of the USA. The
most common usage is for foilback imitations of diamonds
and other gemstones.
ROUGH - Any uncut
or unpolished gem material.
- The display of reflections from a stone as the stone, the light source
and/or the observer moves.
SHEEN - The effect
of a mineral's body texture on its surface appearance.
- Any substance fashioned to imitate the appearance of a gemstone.
SINGLE CUT -
A brilliant cut (round) with eighteen facets: 8 bezel, 8 pavilion, a table
and a culet facet.
SOLITAIRE - A
term referring to a ring containing a single diamond or other gem.
STABILITY - The
ability of a gemstone to resist loss of color, dissolution by chemicals
and other forms of deterioration.
STAR FACETS -
The eight triangular facets that bound the table of a round, brilliant
In gemology, any substance represented to be or used to imitate a more
SYNTHETIC - A
manmade gem material that has essentially the same physical, optical and
chemical properties as that of its natural counterpart.
- The horizontal, top flat facet on the crown of a faceted gemstone.
TARNISH - Tarnish
is the various degrees of surface discoloration of minerals or metals.
Tarnishing is a mild, natural form of oxidation that is caused by a chemical
variation of the surface molecules due to dust, dirt and/or exposure to
air, especially air that contains traces of sulphurous fumes.
- A former name for the kite shaped facets
that are cut and polished on the top crown of brilliant cut gemstones.
STONE AND NEEDLES - A set of tools used to
test the gold content of a particular item. A black stone is streaked with
the item and several gold tip needles of various karat values. Acid is
poured onto the stone and the gold tip needle streak that dissolves at
the same rate as the jewelry item's streak is the correct karat gold of
CRYSTAL SYSTEM - Crystal growth formed by
three axes created at right angles to each other. A gemstone with this
type of crystal formation is zircon.
- The metric measurement of a brilliant cut
gemstone that is measured from the stone's top table to its bottom culet.
RING - Thumb rings were first used in the
orient (China) during the K'ang Hsi period (1662-1772). They were made
of jade, bone, ivory or glass and used by archers to protect their thumbs
as they pulled the string of the bow back into the hold position to release
the arrow. Over time, the rings slowly became fashionable as a body adornment.
- Invented by Charles L. Tiffany in 1886, it is the style of setting a
single diamond (solitaire) into a ring using a flared prong to secure the
stone. The setting usually consists of 4, 6 or 8 prongs that bend slightly
over the girdle of the gemstone to keep it secure.
- A technique of enhancing or neutralizing
a gemstone's color. Enhancing a gemstone involves painting the pavilion
facets of the stone to improve its color. Neutralization is used to tone
down the yellow of a diamond. This is
done by painting violet dye around the girdle of a diamond (or also the
pavilion facets). It has been used since the 16th century, even prior to
the origin of the brilliant cut. Tinted gemstones are usually set in a
closed setting to hide the fact that the stones have been altered.
- An attribute of color which determines its lightness or darkness of shading.
- A tool that disperses heat by using various gases mixed with oxygen.
The cleanest torches use natural gas, propane, and hydrogen.
- The opposite of brittleness. It is the ability of a mineral, element,
crystal or gemstone to resist breakage (fracturing) when struck. Toughness
is not the same as the hardness of a stone.
- Types of metals that because of their atomic structures allow absorption
and refraction of light in a variety of degrees. Such elements are titanium,
chromium, copper, cobalt, iron, manganese, vanadium and nickel.
- Passing light imperfectly through a gemstone; blurry or cloudy.
- The ability of a substance to transmit light. In gem testing terms transparency
is called " diaphaneity." The degrees of transparency are:
- The object clearly transmits light. Transparent substances include quartz,
diamonds, and glass.
- There is no clear vision through the gemstone. Examples include jade
and green onyx.
No light is able to pass through the substance.
- A diamond that has been irradiated,
neutron-treated, cyclontroned, electroned, exposed to radiation (radium
bromide), or given any other modern treatment. In some cases, these processes
are used to color the diamond so that it will appear as a shade of blue,
green, red, yellow, orange, brown, black or pink. Other processes are used
to bleach the stone of any color. The first experiments using these processes
took place in 1904 and were done by Sir William Crookes. His first colored
diamonds were done by radiation and his green stones are still radioactive
to this day. Lab tests can distinguish if a diamond has been treated.
- Specific gems that have three distinct colors because they formed near
various minerals which colored a specific area of the original crystal.
An example of a tri-colored gem is a "watermelon tourmaline."
TRIGONAL OR (RHOMBOHEDRAL CRYSTAL
SYSTEM) - One of three-fold symmetry crystal
growth or uniaxial. Many gemstones commonly used in jewelry have this type
of crystal system. Examples include as tourmaline,
quartz, calcite and corundum.
- A deltoid shaped and faceted gemstone. More specifically, it is a gemstone
that has an arched shaped triangle cut with 25 facets on the crown and
19 facets on the pavilion.
- A fossil marine animal of many varieties
and sizes that is used for jewelry and by collectors as a unique example
of early geological periods. You can see many examples of these unusual
creatures at Ralph Miller Jewelers.
- A technique of combining various or similar gemstones in three layers
to create an imitation gemstone. For example, an opal triplet is a thin
layer of opal sandwiched between a quartz
top and a colored matrix backing material such as black onyx. It is held
together by gem cement or gelatin to enhance the color. Please note that
extreme care must be taken in cleaning any jewelry that has a triplet or
doublet (two layers of material) mounting. Do not soak them in any jewelry
cleaner or use an ultrasonic cleaner. Please see our proper care
and cleaning section on this web site.
- A polishing abrasive for metals often used as a preliminary cleaning
tool to remove filing marks before the final cleaning of the item using
- A weight unit for precious metals predominately used in England and the
United States. Twenty pennyweights (dwt) equals one troy ounce and twelve
troy ounces equals one troy pound.
- A technique of polishing ordinary quality gemstones. The stones (hopefully
all of the same hardness) are placed within a barrel. This barrel is then
revolved and spun to combine the stones with water, grit or polishing powders.
It was used in the 1600's prior to the technique of faceting.
CRYSTALS - Two or more mineral crystals that
have grown together in a symmetrical nature, usually nonparallel. Sometimes
called twinned crystals.
CLEANER - A machine commonly used by jewelers
to clean jewelry effectively. The ultrasonic vibrations free most types
of dirt, grime, and oils from the items. Some ultrasonic cleaners come
with a heating unit to also add heat to the cleaning procedure. When using
this type of cleaner extreme care is recommended because certain gems can
not withstand the heat and vibration. (Please consult this web site's cleaning
recommendations for each specific stone).
LIGHT - Light that is invisible to the naked
eye because it consists of wavelengths shorter than those of visible light.
- Minerals (crystals) that have the unique property of single direction
refraction or one optic axis. Because of this cutters must align rough
pieces for proper visibility of the light reflection when preparing the
gemstone. The stone's brilliance can be lost if axis alignment is not carefully
- Silver overlaid with gold (gold plated silver).
ENAMEL - A fine ground power of various colored
glass that when heated in the correct procedures will permanently adhere
to metals to create decorative colors and patterns.
- The metric measure for gemstones and jewelry that uses the carat as its
base. The carat is further broken down into points and grains. It was first
used in 1913.
GRIND - A technique of grinding stones using
water as a lubricant. Historically, a mixture of water, clay, salts and
enamel frit (small pieces of glass) was used. Using this mixture, decoration
was added to the piece by dipping or spraying it onto the object before
it was fired.
GOLD - An alloy of yellow gold which has silver,
zinc, or platinum as a whiting agent.
OPAL - A type of opal, usually associated
with precious white opal found in Australia, that contains a variety of
colors and flash plates.
- Electro-magnetic radiation. Used by man as a treatment for some stones
to enhance their beauty.
GOLD - A specific color of gold when its in
its natural state.
CUT - A type of a brilliant cut that adds
an extra 16 small facets at the bottom of the pavilion cuts (near the culet)
that can increase a stones brilliance.