This Gemstone and Diamond Dictionary is presented by
request. While there are several gem-focused glossaries or dictionaries
available on the internet, I have been requested to add my version to this site
for your convenience.
This list has been compiled by looking at
definitions on other dictionaries and glossaries. Where I judged a
definition to be unclear, geared too much toward marketing, or otherwise
lacking, I have edited that definition.
I have done so sparingly, to promote standard
Adamantine Refers to the diamond-like luster
of a gemstone. Gemstones with a diamond-like luster include diamond (of course),
demantoid garnet and sphene
The appearance of a floating, billowy light in cabochon gemstones or a
stationary sheen on the flat surface of a gemstone. Seen in certain Feldspars
such as Moonstone. Schiller.
Deposits Gem deposits found in water
after they have been separated from the mother rock.
Stone Any stone that has been
changed in appearance, particularly in color, by an artificial process. Also
referred to as an Enhanced Gemstone or a Treated Gemstone. Heating, irradiation,
and dyeing are among the processes used to change gemstone appearance.
Amethystine The color violet to purple
in a gemstone..
Amorphous Gemstones without a crystal
structure are referred to as amorphous. These include gems such as amber, coral,
opal and pearl
Incidence The angle at which a ray of
light enters a stone as measured from normal.
Reflection The angle at which a
reflected ray of light leaves a surface as measured from normal.
Refraction The angle at which a
reflected ray of light leaves a surface as measured from normal.
Anisotropic Term used in gemology for
Stone A man-made, imitation of a
gem. Neither a natural nor synthetic gem.
Asterism The appearance of a rayed
figure or rayed star in a gemstone, caused by the reflection of light from
minute inclusions. Star Sapphires and Star Rubies are two well-known examples of
gemstones featuring a rayed star.
Aventurescence A glittery appearance of the
surface of a gemstone, caused by the reflection of light off small mineral
inclusions. Aventurine Quartz and Goldstone (glass) both have aventurescence.
style of step cut used for small gem materials.
Baroque May apply to certain
gemstones or pearls. Either a gemstone or pearl with an irregular shape, such as
Tumbled Stones or Baroque Pearls.
Base The pavilion (The portion of
a facetted gemstone below the Girdle.)
Baton The English name for the
Bead A hollow gemstone, usually
round. Designed to be strung.
Setting A method of securing a
facetted stone. A small burr of metal is raised with a graver and worked to the
edge of the stone. This burr is then burnished with a concave tipped punch into
a small ball over the girdle of the stone. Normally used to secure very small
gemstones, usually in multiples.
Bearing The supporting ledge of a
Treatment A form of heat treatment for
sapphire that adds the element beryllium to the heating process. Beryllium is an
element well known in the gem world, since it is an essential constituent in
many gemstones, including emerald, beryl, and aquamarine. When sapphires are
heated with beryllium, the result is a reduction in blue tones. Thus bright
yellow or orange sapphire can be produced from weak yellow or greenish gems.
Some stunning colors have been produced using this method.
Beryl Emerald, aquamarine and
other aluminum beryllium silicate minerals.
Bezel A thin strip of metal that
holds a gemstone in place. Used in place of prongs.
Biaxial A double-refractive
gemstone, which has two directions of single refraction or optic axes.
Bi-color A gemstone exhibiting two
color zones, such as ametrine or many tourmalines.
Birefringence The numerical measurement of
double refraction in gemstones.
Birthstone The association of gemstones
with astrology goes back centuries. More recently,
on the surface of 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. Blue-White According
to the Federal Trade Commission, only diamonds with a distinct blue body color
may be traded as "blue-white." For many years the term referred
to a diamond without a distinctive body color, however misuses of this term have
rendered it almost meaningless.
Blocking The process of placing the
facets on a stone.
Appearance The optical characteristic
of a gem produced by internal inclusions, fractures or layers.
Color The dominant hue within a
Setting A method of stone setting in
which the gem is enclosed in a box and the edges of the metal are pressed down
to secure the stone.
Brilliance The total amount of white
light returned to the viewer by a gem. This includes internal and external
most common style of diamond cutting, also used for many other gemstones, which
consists of a combination of triangular and kite shaped facets. The round
brilliant cut features 57 or 58 facets.
Stone/Bristol Diamond Old trade-term for colorless
crystal quartz. Also a trade name for colored glass immitations, Bristol Glass
Bruting A method of rough-diamond
fashioning by rubbing one diamond against another.
Cabochon A gemstone with a domed form. The oldest form of gem cutting.
Calibrated Many gemstones are sold in
calibrated or standard sizes that will fit commercial jewelry settings. Standard
sizes are calibrated in millimeters for a number of different gem shapes.
Cut Gemstones cut to a specific,
standardized size for mounting. Also, small gem material cut for pave' setting.
Cameo A gem or shell
material--usually with two or more distinct colored layers. The top layer is
carved in relief and the bottom layer acts as a contrasting background.
term referring to diamonds with an intense yellow hue. The term "fancy
yellow" is often used if the yellow makes the stone very distinctive.
Carat A unit of weight measure for
black-appearing inclusions in a diamond caused by the of other mineral crystals,
such as garnet.
Cat's Eye A
gemstone that displays a thin band of reflected light on its surface when
cut as a cabochon. Chatoyancy.
Chatoyancy The appearance of
well-defined bands or The
appearance of well-defined bands or threads of light across the surface of a
Center Stone The center stone is the
prominent center piece in a jewelry setting that has multiple gemstones. See
also Side Stone.
Color A phenomenon seen in some
gems which have a different color in natural light than in artificial light. The
color-change is caused by selective absorption and transmission of light.
Alexandrite has become a very well known color-change gem, but other gemstones
may exhibit the phenomenon.
Chanthaburi The city in southeastern
Thailand famous as one of the world centers for gemstone processing and trading.
Chanthaburi is also famous for its weekend gemstone market.
Chatoyancy The appearance of
well-defined bands or threads of light across the surface of a gemstone. This
appearance is caused by the reflection of light off small parallel mineral
inclusions. May appear as a single-band chatoyancy--Cat's Eye--or a series of
Checking The tendency of Opals to
crack when exposed to heat or drying air. Also known as Crazing.
Chevee A gemstone with a smooth
Chip A popular, common name for a
small rose-cut or single-cut gemstone.
Clarity Referring to a stone's lack
of inclusions or other visual defects.
Clarity Grade One of the 4 C's. Grades
range from F (flawless) through several grades of I (included).
A stone setting of projecting metal claws which grip the stone at--and just
Clean A trade term for gemstones
which are free of noticeable flaws.
Cleavage A smooth, flat break or
separation in a gem along the direction of its atomic structure.
Cloudy A group of small, white
inclusions that give a cloudy appearance to a diamond.
Setting Closely set gemstones
arranged to give the illusion of a single, larger gemstone.
Stone A gemstone covered by an
artificially applied transparent material to enhance its color. Often used with
Cobbing The removal of undesired
material from a piece of gem rough.
Set A variation on box setting
in which the sides of the box are filed away to sallow more light to enter the
Color Used in the evaluation of a
gem. The quality of a gem can based on either the presence or the absence of
Gems Color change gems change
color due to changing light conditions (such as alexandrite or color change
sapphire) or when viewed from different angles (such as andalusite or iolite).
Grade One of the 4 c's. Diamonds
are ranked on a scale from "D" (colorless) to "Z"
(noticeable tint of color, typically yellow or brown). Diamonds with saturation
greater than "Z" color are considered Fancy Colored Diamonds and are
graded on a separate scale. Color
Zoning Uneven color in gemstones in
irregular patches. Can be either different colors or different tones of the same
Stones A gemstone other than a
Cut Traditional gem facets are
fla.. Concave cutting creates facets that are curved or scooped. These curved
facets refract more of the ambient light and return it to the eye as brilliance.
Concave cutting is a recent innovation dating back to the early 1990's. It
requires considerable expertise and results in higher weight loss to the rough
stone, since more material must be cut away to create the curved facets.
Copper-bearing Gemstones that contain traces
of copper are very rare and typically have a intense blue, blue-green or violet
color. There was considerable excitement in the gem world when the first
copper-bearing gemstones were discovered in 1989. See also Paraiba.
Corundum Sapphire and ruby. A
crystalline form of aluminum oxide.. It is naturally clear, but can have
different colors when impurities are present. Corundum is much admired for its
hardness (9.0 on the Mohs
scale) and brilliance and excellent wearability.
Crazing The tendency of Opals to
crack when exposed to heat or drying air. Also known as Checking.
Angle Greatest angle measured from
normal at which light can be refracted out of a stone. Small angle at which
light is totally internally reflected.
Crown The part of a facetted
gemstone above the girdle.
Setting A collet setting consisting
off a flared cylinder with one end of the cylinder notched to form prongs.
Cryptocrystalline Extremely small crystals
which cannot be seen separately, even under high magnification.
Crystal A solid made up of atoms,
bounded by natural planar surfaces.
System The classification of
minerals according to the geometric form in which their crystals grow. Each
mineral has a distinct system--Isometric, Tetragonal, Hexagonal, Orthorhombic,
Monoclinic and Triclinic.
Crystalline Having a regular crystal
Crystallography The science of the internal
structure of crystals.
System The Isometric crystal system
which consists of three axes, each of equal length and perpendicular to others.
zirconia A lab created diamond
simulant, often abbreviated as CZ. While CZ is a transparent stone, trace
elements can be added to the manufacturing process, producing a wide range of
colors. On Mohs scale of hardness, CZ is harder than other gemstones except for
diamond, ruby, sapphire and chrysoberyl. Not to be confused with Zircon, a
Culet A small polished surface
placed at what would be the point or ridge of a facetted stone, used to reduce
Cuprian Copper bearing.
Cut One of the 4 C's. The angles
and proportions of a gem. The placement of facets. Example - round brilliant
Cuvette A raised relief carved into
a gemstone in a concave depression.
Demantoidi a rare and valuable andradite
It exhibits a range of greens from dull to bright emerald green and on rare
occasions displays yellow. On Mohs scale of hardness, demantoid is relatively
soft at 6.5. It has an adamantine luster.
Density Mass per unit volume. The
amount of matter in a given space. The higher density/atomic mass of a gemstone,
the more it weighs for a given size.
Dentelles An early term for glass
imitation stone without foil backing.
mineral that crystallizes in the cubic system and is composed of carbon with a
hardness of 10, a refractive index of 2.417, and a specific gravity of 3.52.
Diamond Cut Also known as the round
Brilliant Cut, the style of cutting a stone with multiple facets to maximize
brilliance. Modern round brilliant cuts have 58 facets.
Dichroism The transmission of two
different colors in two different optical planes as light passes through a
gemstone. May be used as a method of distinguishing one type of gemstone from
Dichroscope An instrument used to view
the light passing through a gemstone to determine the presence of dichroism.
Treatment A form of heat treatment that
adds one or more chemicals to the heating process to change the color of a
gemstone. Typically the treatment does not penetrate deep into the stone, so
gems treated in this way cannot be recut. Diffusion treatment is a standard
treatment to increase the asterism effect in star sapphire.
Dispersion The separation of light into
its spectral colors as it passes through a gemstone.
Dodecahedron A twelve-sided geometric
solid. One of the crystal forms found in the Isometric crystal system.
Refraction The separation of a beam of
light into two separate beams as it enters a gemstone. The two beams travel at
different speeds. May be used to distinguish one gemstone material from another.
Occurs in all crystal systems except Isometric.
Doublet An assembled stone of two
parts. Colorless cement or heat is used to join the parts together. Often used
Durability The combined characteristics
of hardness, toughness and stability in gemstones. One of the deciding factors
in gemstone value.
Stone A gemstone to which an
artificial stain is added to improve color or to imitate a more valuable
Face The plane surfaces which
form the sides of a crystal.
Facet A planar surface which is
polished onto a gemstone.
Cut/Fancy Shape Any style of gemstone
cutting other than the round brilliant or single cut.
Diamond Any diamond with a body
color strong enough to be attractive.
Feather A trade term referring to
any inclusion within a gem, usually a jagged irregular fracture which appears
Inclusion Liquid and/or gas or solid
flaws in gemstones which align in the form of a human fingerprint.
Finish The quality of a prepared
surface. In facetted gemstones, the placing of the facets and the quality of
polish. In cabochon gemstones, the quality of the polish.
Fire The play of color on or
within a gemstone as a result of dispersion. Prominent valued feature of Opals
and Fire Agates.
Fissure A surface crack on a
gemstone. Gems with fissures may be Fracture Filled.
Flaw Any visible imperfection
within a gemstone.
Fluorescence The emission of visible
light when a gemstone is exposed to ultraviolet light. Used a method of
distinguishing one gemstone from another and a natural gemstone from a synthetic
Backed The adding of a layer of
metallic foil to the back of a gemstone to improve its color or brilliancy.
Fracture A break or chip in a
gemstone in any direction other than along a cleavage plane.
Filling Applying a material
that will allow the light to pass through smoothly. Different materials are
used; oil, wax, glass, epoxy, and borax are common materials. The most commonly
filled stones are emerald,
Full Cut A round-shaped, brilliant-cut
gemstone having 58 facets.
mineral or organic material with sufficient beauty, rarity and durabilityto be used as a jewel when cut and polished.
Gemology The study of
gemstones--identification, grading, appraisal, marketing, and fashioning.
Geode A rock which contains a
cavity lined with mineral crystals.
Girasol A gemstone with a glowing,
milky sheen that moves as the stone is moved in the path of a light source.
Girdle The outer edge of a
Glyptic The art of engraving or
(luster) One of the the technical
terms used to refer to the luster of a gemstone. Jadeite is an example of a gem
with a greasy luster.
Group Two or more chemically
related gemstone materials, similar in structure and physical properties.
Setting A setting in which the crown
of a gem is the only portion exposed and the table of the gemstone is nearly
level with the surrounding metal. No prongs or separate bezel is evident; all
means of setting the gemstone are below the metal's surface.
Habit The most common form in
which a mineral occurs.
Hardness A gemstone material's
ability to resist scratching.
Head An added finding to mount a
gemstone in a prong setting.
Heat-Treatment Heating a gemstone material
to improve color.
Liquid A liquid of known specific
gravity, used to test the specific gravity of a gemstone.
System A crystal system which
consists of four axes, three intersect at a 60-degree angle of each other while
the fourth is perpendicular to the other three.
Hue the dominant wavelength of
color attributed to a gemstone. There are six primary hues: violet, blue, green,
yellow, orange, and red. In between these primary hues are secondary hues, such
as blue-green. See also tone and saturation
Karat Karat (as distinguished from
Carat) is a measure of the purity of gold. Most gold jewelry is actually made
from a gold alloy containing gold and another metal or metals. 18K gold, for
example, is 75% pure gold.
Make A trade term referring to
the quality of a gemstone's cut.
Marquise The marquise shape is an
elongated oval with points on both ends
Matrix The rock in which gemstone
material is found. Some matrix material may remain in a finished gemstone--the
veining in turquoise is a common matrix seen in a finished gemstone.
Melee Gemstones of approximately
.18 carats or less. May refer to all gemstones or cutting styles, but is usually
used for round, facetted diamonds.
(luster) One of the technical terms
used to refer to the luster of a gemstone. A gemstone that is reflective like
polished metal is said to have a metallic luster. Hematite is one of the rare
Millegrain A style of setting in which
the stone is held in place by a row of tiny beads along the girdle of the stone.
Mineral Inorganic substances
occurring naturally and having a definite chemical composition and crystal
Mineralogy The study of minerals,
including their physical and chemical properties.
Mixed Cut A gemstone cut consisting of
a brilliant-cut crown and step-cut pavilion.
Hardness Scale A categorization of minerals
according to their hardness--resistance to scratching. Diamond is the hardest
and talc is the softest.
comparative scale of hardness is 1) talc
8) topaz and beryl
Moissanite A lab-created diamond
simulant based on the structure of natural moissanite. On Mohs' scale of
hardness, moissanite is 9.5. It has more brilliance, fire and luster than any
hard jewel on earth, including diamond.
System A crystal system which
consists of three axes, each unequal in length with two intersecting at oblique
angles and the third perpendicular to the other two.
Mounting The portion of a piece of
jewelry which holds a gemstone.
Nacre The iridescent substance
secreted by a mollusk during the formation of a pearl that consists of layers of
aragonite and calcite crystals.
Natural A trade term for a portion of the original surface of a rough diamond left
by the cutter when polishing and faceting a diamond. Naturals are usually found
near the girdle of a diamond and are represented in green on a plotting diagram.
Natural Gemstone A gem produced by nature.
- A pearl that originates naturally in a mollusk, as distinguished from cultured
or imitation pearls.
NICK - A minor chip on the surface of a diamond, usually found near or on
the girdle of the stone
Normal In the study of light, an
imaginary line perpendicular to a surface. Used in gemology to describe the
angle at which light strikes an object.
Padparadscha Derived from the Sinhalese
term for "lotus flower," padparadscha refers to a lush pink and orange
sapphire resembling the color of the lotus. Padparadscha is also sometimes used
to refer to other types of gemstones, such as topaz and tourmaline, with this
Paraiba A rare copper-bearing
tourmaline with an intense blue or blue-green color, first found in the state of
Paraiba in Brazi. There have been recent finds in Nigeria and Mozambique of
similar material, and the term "paraiba" is now used to refer to all
examples of this copper-bearing tourmaline. See also Copper-bearing.
Parting Flat, smooth breakage of a
mineral along planes or twinning, commonly found in corundum.
Paste Glass usually containing
lead oxide and cut to simulate a gemstone.
Pave' Small stones set in the
surface of metal as close together as possible.
Pavilion The portion of a facetted
gemstone below the girdle.
Shape Resembling a pear or
teardrop, this fancy gem shape is rounded on one end and pointed on the other.
Phenomenon An optical effect which
appears in certain gemstone materials. Often revealed by or enhanced by proper
Phosphorescence A continuing glow exhibited
by some gemstones after the source of illumination has been removed.
Blood Refers to the most prized
color of red in rubies. Pigeon's blood red is thought to be a pure red with a
hint of blue. It is associated most with rubies from Burma, though any ruby
could be this color.
Color Prismatic flashes of color
seen within a gemstone. The color display in Opal.
Pleochroism Change of colors observed in
double-refractive gemstones when viewed different directions. Selective
absorption and varying transmission rates of light cause the color change when
the gemstone is viewed along different optical axes.
Point A gemstone unit of weight
equal to 1/100 of a carat.
smoothness of the surface of a fashioned gem in which optical reflection is
maximized and shows no visible wheel or burn marks.
Cut The portuguese cut refers to
a particular type of faceting where the gem is cut with two rows of rhomboidal
and three rows of triangular facets above and below the girdle. The Portuguese
cut thus has an extra row of facets on the crown, and this style enhances the
brilliance of the gem. The Pportuguese cut is one of the most popular fancy cuts
in the market and you'll find many varieties of gems cut in this style.
(gemstone) Traditionally, the four
precious gemstones are diamond, ruby, sapphire and emerald. Today, the
distinction between precious and semi-precious gems has been rejected by some
gem trade associations.
Prong A narrow tab of metal folded
over the girdle of a gemstone to secure it in a setting.
Saturation Saturation is one of three
characteristics used to describe the appearance of color. Saturation (also known
as intensity) refers to the brightness or vividness of a color. See also hue and
(gemstone) An outmoded term for gems
other than diamond, emerald, sapphire, and ruby.
Scarab A gemstone cut in the form
of a beetle.
Schiller The appearance of a
floating, billowy light in cabochon gemstones or a stationary sheen on the flat
surface of a stone. Seen in certain Feldspars such as Moonstone. Adularescence.
Scintillation Reflections from a polished
surface as its relative position to either the viewer or the source of
Scrimshaw Carved or engraved ivory or
vegetable ivory. The engraved lines and textured surfaces are often colored with
inks and dyes.
Setting A mounting or the portion of
a mounting which actually holds the stone.
Shape Gems are fashioned into many
shapes, such as round, triangle, pear, oval, and many more. A round shaped
gem may be cut in any of several styles... for example, brilliant cut, or
effect resembling luster, and is caused by light reflection from inclusions or
texture inside the gem. Luster is light reflected from the surface of the gem
and sheen is reflection from inside the gemstone
Side Stone Side stones are set around or
beside the center stone in a jewelry setting.
Single Cut A stone with
seventeen facets or fewer.
Most gemstones are doubly refractive -- they have 2 refractive indices. Only a
few gemstones have a single refractive index, specifically diamond, spinel and
garnet. See also Birefringence.
single stone in a simple setting. Compare Center Stone and Side Stone.
Species The term used to designate a
family of gemstones. For example, corundum is a species that contains the
varieties sapphire and ruby. The Quartz family contains amethyst, citrine, and
chalcedony, to name a few
Stability The ability of a gemstone to
Stone A gemstone in which the
phenomenon of asterism is visible as four or more rays.
Strain Irregularity in the ordered
structure of the atoms in a crystal.
Strass Glass containing a high
amount of lead oxide and cut to simulate a gemstone. Named for its inventor
Substitute A substance used to imitate
a more valuable gemstone. The substitute substance may be natural or man-made.
Swiss Cut A gem cut consisting of
Synthetic A man-made gemstone that has
nearly the same physical, optical and chemical properties of a natural gemstone.
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. When using this type of cleaner, extreme care is
recommended because certain gems cannot withstand the heat and vibration.
Light Light that is invisible to
the naked eye because it is emitted in wavelengths shorter than those of visible
Stone A gemstone possessing one
optical axis. Crystals of the hexagonal or tetragonal system are uniaxial.
Waxy One of the technical terms
used to refer to the luster of a gemstone. Turquoise is an example of a gem with
a waxy luster.
Window In a well cut faceted gem,
the pavilion facets (those on the lower half of the stone) should reflect light
back out the top or table of the stone. If the facets are cut below the critical
angle for the particular material, light will pass right through the stone
instead of being reflected back towards your eye. When this happens the gem will
lack sparkle and brilliance
Zirconium silicate. Gem zircon occurs in many colors.
zoning) A term that describes the uneven distribution of color in a gemstone.
Zoning is best seen when looking at the stone through the table facet.
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Gem Industry News...
Zimbabwe Diamond Fields
The diamond fields of Zimbabwe are the scene of many human rights abuse
reports, according to diamond trade news reports..
Over the past couple of years Zimbabwe has experienced horrific political
conflict and massive economic inflation that has totally destroyed the value of
the country's money.
I'm told that this environment has contributed to harsher worker conditions
and government regulations.
The international diamond community is threatening sanctions on Zimbabwe's
ability to participate in the diamond market because of these abuses..
Our friend Bill lives in Zimbabwe, where he is a farmer, safari guide, and
colored gem cutter. He states that he hears that conditions in the diamond
fields are bad, but he doesn't go near those places.
He hears this from people that come looking for work. He doesn't have work
for all of them... but he looks the other way when they sneak into his fields at
night to eat his tomatoes and such.
An ailing economy is an opportunity for independent jewelry dealers.
People still want and need jewelry. Gift occasions, people building and
refreshing their wardrobe, and see it - like it - buy it purchases are
all sales opportunities for you.
An ailing economy isn't a deal killer when you offer quality, service, and