abraded culet. When the small culet facet becomes chipped or scratched by another diamond.
abrasion. A bruise or scratch on a fashioned diamond.
adamantine. The lustre of diamonds.
alluvial deposits. All deposits laid down on land by the agents of erosion, including streams, wind, waves and glaciers.
Amsterdam. A cutting centre in the Netherlands.
anisotropic. Crystalline substance that is doubly refractive.
Antwerp. The most important diamond-cutting centre in the world and a major distribution centre for polished goods (Belgium).
appraisal (of diamond). A monetary evaluation of a diamond or diamond jewellery, usually for insurance or estate purposes. An insurance appraisal is based on an estimate of retail replacement value, and an estate appraisal an estimated realization from a quick sale. An appraisal leaves no room for misinterpretation only when it describes the piece in detail, giving carat weights, exact measurements of stones, colour and clarity grades, all proportion characteristics and plots of any inclusions, flaws or blemishes on or in diamonds or other gemstones above melee size. This affords protection in the event of loss or damage.
Arkansas. A source for rough diamonds in the U.S. known as "Crater of Diamonds State Park" to which the public is invited to search for diamonds for a fee.
atomic structure. The arrangement of atoms in a pattern which when repeated in three dimensions forms a crystal.
Australia. The largest source of rough diamonds in the world, not necessarily gem quality. Fancy colour diamonds like champagnes, cognacs, coffees, pinks and yellows come from Australia.
baguette. A style
of step cutting for small, rectangular-shaped gemstones, principally diamonds.
bearded girdle. If a diamond is rounded up too quickly in the fashioning process (bruting), the surface of the girdle will lack the smoothness and waxy lustre of a finely turned girdle. Consequently, numerous minute, hairline fractures extend a short distance into the stone.
belly. The central area of a marquise, oval or pear-shape diamond, when viewed face-up.
bezel. 1) A kite-shaped facet on the crown of a fashioned diamond. 2) A type of setting where the metal surrounds the gemstone and covers the girdle.
binocular microscope. A magnifier equipped with twin objectives & oculars
and provides three-dimensional viewing.
black diamond. 1) When a diamond is dark gray or truly black. Such a stone may be opaque to nearly semi-transparent. 2) A misnomer for hematite.
blemish. A term used to refer to a surface imperfection on a fashioned diamond; e.g. a nick, knot, scratch, abrasion, poor polish, also a natural on the girdle or an extra facet.
blue diamond. A diamond with a distictly blue body colour, even though very light in tone, is a fancy diamond. A blue body colour may also be induced artificially. See Bombarded Diamonds.
blue ground. A miner's name for kimberlite, the rock that contains diamonds.
body colour. The colour of a diamond as observed when examined under diffused light against a hueless background free from surrounding reflections.
bombarded diamond. A diamond that has been subjected to bombardment by fast electrons, neutrons, deutrons, etc. The purpose is to make the colour of a diamond more attractive and desirable.
boron. Element of atomic number 5 (B). Cause of semi-conductor properties and the blue colour in Type IIb diamonds.
Botswana. Source for largest gem quality rough diamonds in the world.
bourse. French, meaning an exchange or meeting place where merchants transact business. Diamond dealers' club.
bow
tie. A darkened area across the centre of a fancy shaped diamond exhibiting
a "bow tie" appearance when viewed through the table. Indication of fair proportions.
branded diamond. A diamond that has under-gone some kind of branding or labelling on it's girdle edge or table facet through laser inscriptions or other patented processes.
Brazil. An important diamond source since the first discoveries were made in 1725.
brilliance. The intensity of the internal and external reflections of white light to the eye from a diamond or gem in the face-up position.
brilliant cut. The combination of triangular and kite-shaped facets on a
diamond or coloured stone, where the most common is round, then other fancy
shapes as oval, pear-shape, marquise, trilliant, radiant and princess cut.
brown diamond. Brown tints in diamonds are next to yellow in occurance, thus they are graded in the same manner in the top grades.
bulge. A bending outward of the pavilion facets of a step-cut diamond beyond the acceptable minimum necessary to achieve the cut.
bulge factor. Deduction for excessive weight retention resulting from bulge on the pavilion facets of a step-cut diamond.
burn mark. A defect in finish grade. It is caused by the burning or oxidation of a diamond polished too rapidly in a mechanical dop.
C. The abbreviation for the element carbon. See Carbon.
canary diamond. A trade term for an intensely coloured yellow diamond. See
Fancy Colour.
carat. A unit of weight for diamonds and other gems. 1 carat = 0.2 grams
carbon. 1) A chemical element C, with an atomic number 6. 2) An inclusion in a diamond that appears black.
carob seed. The origin of the "carat weight".
cavity. A large indentation (chip) on a diamond's surface that may be caused by cleavage, by a blow, or by a pulled out knot or included crystal.
certificate. A written report describing a diamond as to its weight, proportions,
colour and clarity grades.
chemical composition (of diamond). Gem diamond is about 99.95% pure carbon. The remaining 0.05% are impurities which may contribute to colour, include iron, silicon, calcium, magnesium, nitrogen, aluminum, and boron.
chip. A small curved break on a diamond that extends from a surface edge.
chipped culet. When the small culet facet becomes chipped, possibly while in contact with other diamonds in a diamond paper.
clarity grade. The
relative position of a diamond on a flawless-to-imperfect scale.
GIA: FL-IF-VVS1-VVS2-VS1-VS2-SI1-SI2-I1-I2-I3
clarity.
cleavage. 1) A crystalline mineral breaking in certain definite directions, parallel to a possible crystal face, leaving a smooth surface, 2) Any break along the grain of a diamond parallel to one of four pairs of octahedral faces.
cleavage crack. A break in a diamond in the plane of the cleavage (feather). It is the most damaging type of imperfection, since it affects durability as well as beauty.
cleaving. The splitting of a diamond along a cleavage plane, into two or more portions of a size or shape in order to produce a fashioned stone.
cloud. A group of tiny white inclusions that together give a clouded appearance in a highly transparent stone.
coloured diamonds. Referred to as "fancy diamonds", occur in yellow, brown, green, blue, pink, red and black.
colour grade. The
relative position of a diamond's body colour on a colourless-to-yellow scale.
GIA colour grading scale: D-E-F-G-H-I-J-K-L-M-N-O-P-R-S-T-U-V-W-X-Y-Z-Fancies
colourimeter. A computerized instrument used to colour grade diamonds. It grades all shapes of diamonds even rough crystals. Limited in some cases.
colourless. A transparent diamond or gemstone completely without body color. comparison diamonds. Same as master diamonds.
covalent bonding. The strongest of chemical bonds and are characterized by great stability, general insolubility, electrical nonconductance, and high melting and boiling points. Diamond is an outstanding example of covalent bonding.
crack. See fracture.
crown. That portion of any faceted gemstone above the girdle.
crown angle. The angle measured between the table and the crown facets.
crown height. The vertical distance between the girdle plane & the table.
crystal. A crystalline solid bounded by natural, plane surfaces, bearing a definite relationship to one another.
crystal form. The geometric shape of a crystal, e.g. octahedron.
cubic (or isometric) system. Diamond crystallizes in this system
culet. The small facet that is polished parallel to the table at the pavilion, sometimes left pointed.
cutting. 1) Fashioning a diamond from rough, the steps include: a) awing, b) leaving, c) grinding, d) bruting, e) polishing, and f) faceting. 2) Synonymous with make (proportions & finish).
cutting centres. The major diamond-cutting centres are: Antwerp (Belgium), Amsterdam (Netherlands), South Africa, New York (U.S.A.), Tel Aviv (Israel), Russia, Bombay (India), and now Australia and Thailand.
dark-field illumination. A method of illuminating diamonds and other gemstones with a strong light from the side while the stone is being viewed against a black background. It causes inclusions and imperfections to stand out clearly.
depth percentage. The depth of a stone measured from the table to the culet, expressed as a percentage of the stone's diameter at the girdle.
diamond.
A mineral composed essentially of carbon that crystallizes in the cubic crystal
system. It is the hardest of all known natural substances (10 on the Mohs scale).
It is the most cherished and highly valued gemstone. It occurs in colours ranging
from colourless to yellow, brown, orange, green, blue, violet, black, pink and
red (extremely rare). High refractive index of 2.417, a dispersion of 0.044,
and a specific gravity of 3.52. diamond, formation of. Under extreme pressure
& temperature existing at a hundred miles below the earth's surface, carbon
crystallizes as diamond. Diamonds are then transported from depth to the surface
in volcanic pipes called kimberlite (or lamporite in Australia). When kimberlite
is exposed at the surface, it decomposes & disintegrates releasing the diamonds
which may be deposited and concentrated in alluvial deposits at the surface.
diamond paper. A sheet of durable paper stock folded to form a pocket in which diamonds or other gems are contained.
dimorphism. The crystallization of a substance into two different crystal systems. e.g. carbon crystallizes in a cubic form as diamond and in hexagonal form as graphite.
dispersion. The property of transparent gemstones to separate white light
into the spectral colours. Also known as "fire".
doublet. An assembled stone usually of two parts, crown and pavilion, cemented or fused together.
drag lines. Irregularities in polish caused by inclusions (knots) at the surface leaving a marking downstream from the object.
eight cut. Also called the single cut which consists of 17 facets.
Ekati. The first Canadian diamond mine located in the Northwest Territories.
electron-bombarded diamond. A diamond whose colour has been changed to blue (or other) by bombardment of fast electrons.
emerald
cut. A cutting style having a cut corner rectangular-shaped girdle outline.
engagement ring.
A diamond ring given by a man to his fiancee in token of betrothal. 
eternity ring. A circlet of small diamonds set in precious metal, usually given at wedding anniversaries.
external characteristic. A general term used to refer to surface imperfections or blemishes. e.g. nick, scratch, abrasion and extra facet.
facet. A plane, polished surface placed on a diamond or gem.
faceted girdle. Small rectangular-shaped facets polished on the girdle edge. An extra feature on some diamonds.
face-up.
A diamond positioned with the table facing toward the viewer.
face-up colour. Colour observed in a gem viewed in a direction perpendicular to the table. With diamonds, colour becomes visible in the face-up position at about "J" or "K".
fancy cut. Any style of diamond cutting other than the round brilliant or single cut. e.g. pear-shape, heart-shape, emerald cut, marquise, princess, trilliant, radiant...
fancy colour. Any diamond with a natural body colour strong enough to be attractive, rather than off colour.
feather. A cleavage or a fracture that has a feathery appearance when viewed by a grader.
finish. Cutting quality is judged by the proportions and facet angles, by the excellence of its polish, the smoothness of girdle surface, the exactness of its symmetry, and the size of its culet.
fire. See dispersion.
fisheye. A diamond with a very shallow pavilion, producing a glassy appearance & a noticeable decrease in brilliancy.
flaw. A general term used to refer to any internal & external characteristic on a fashioned diamond. Also known as an imperfection.
flawless (Fl). A diamond without internal or external flaws or blemishes.
fluorescence. A variety of luminescence. The property of changing one kind
of radiation to another.
foilback. A piece of faceted glass backed with a thin leaf of metallic foil, to simulate brilliancy of a diamond.
four C's. Quality factors affecting diamond value to 4 terms: carat weight, colour, clarity and cut.
fracture. The chipping or breaking of a stone along a direction other than a cleavage plane. e.g. conchoidal, splintery, granular, even and uneven. Diamonds fracture in conjunction with cleavages, forming an irregular step-like pattern.
fracture filled diamond. An enhancement technique using an unknown substance that fills internal characteristics via a surface-reaching fracture. Note: this enhancement is not permanent, and full disclosure, to the condition of the diamond, to the customer.
frosted girdle. A girdle with a frosted appearance.
full-cut. A brilliant
cut diamond with the total of 58 facets. 
gem. 1) A cut and polished stone that possesses the necessary rarity, beauty and durability for use in jewellery, 2) A term often applied to an especially fine specimen.
Gemological Institute of America (GIA). A nonprofit, endowed, educational institution controlled by jewellers & maintained for the benefit of the industry and the public.
gemologist. A specialist in gem materials. One who has successfully completed
recognized courses of study in gem identification, grading and pricing, as well
as diamond grading and appraising.
gemology. The science and study of gemstones; their sources, descriptions, origins, identification, grading, and appraising.
girdle. The outer edge of a fashioned stone; the dividing line between the crown and pavilion.
girdle facets. The 16 upper- and 16 lower-girdle facets that adjoin the girdle of a round brilliant cut stone.
girdle thickness.
The width of the outer edge of a fashioned stone.
Thickness scale: very thin, thin, medium, slightly thick, thick, very thick,
and extremely thick.
Graguate Gemologist or G.G. One who holds the Graduate in Gemology Diploma, awarded by the GIA.
grain. One-quarter of a metric carat (0.25 ct. or 0.05 grams), a unit of weight commonly used for pearls & sometimes for other gems.
growth markings. Characteristic markings on crystal's surface.
habit. The characteristic crystal form, including distinguishing irregularities, of a mineral. Characteristic habits of diamond are usually octahedral, cubic, dodecahedral, and hexoctahedral.
hardness. The resistance of a substance to being scratched. A series of ten common minerals were chosen by the Austrian minerologist F. Mohs in 1824 as a scale, by comparison where the relative hardness can be told. Diamond is rated 10 on the Mohs scale of hardness, 10 to 150 times as hard as corundum (hardness of 9).
The
following minerals arranged in order of increasing hardness is known as the
Mohs scale of hardness:
|
1.
|
Talc Comparison of Mohs relative hardness scale and absolute measurements of hardness *Diamond
is extremely hard and |
 |
 |
Consumer
Facts: - A hardness of 7 and higher is recommended for gemstones worn in jewellery. |
|
| - Gemstones with hardness greater than 5.5 can scratch glass. |
head. The heel or rounded end of a pear-shaped stone.
heart-shape brilliant
cut. A cutting style having a heart-shaped girdle outline. 
heat conduction. Diamond has a very high thermal conductivity, the highest of any known material which is why they initially feel cold to the touch.
heat, effect on diamond. Transparent diamond will burn between 690 to 875 degrees Celcius. The heat from a torch may cause the surface of a diamond to become leaden & cloudy, but can be corrected by repolishing.
heat treatment of diamond. An irradiated diamond that has turned green may changed to other colours by heat treatment.
high shoulders. On a pear-shaped stone gives the head or heel a flattened appearance.
Hope diamond. The 45.52 carat dark blue Indian stone is one of the world's most celebrated diamonds. Now displayed at the Smithsonian Institution in Washington, D.C.
hydrostatic weighing method. The formula for specific gravity is: SG = weight in air wt. in air - wt. in water The S.G. of diamond is 3.52
I. The abbreviation for imperfect.
IF. The abbreviation for internally flawless.
illusion setting. Setting in which a stone, usually a small diamond, is set in a large polished or reflective plate fixed by claws in order to increase its apparent size.
imitation. Anything that simulates a genuine gem.
imperfect. An imperfect diamond contains imperfections that are visible face-up to the unaided eye or that have a serious effect on the stone's durability.
imperfection. Any internal or external flaw or blemish on a fashioned diamond.
included crystal. A crystal of diamond or other mineral enclosed during the growth process of the main diamond crystal. It may be transparent or dark in appearance.
inclusion. Any visible internal characteristic, such as: bearding, bruise, cavity, chip, cloud, feather, grain, crystal, indented natural, internal graining, knot, laser drill hole, needle, pinpoint, and twinning wisp. industrial diamond. Refers to nongem-quality diamonds that are suitable only for industrial tools, abrasives, drills, etc.
Inclusion Locator Chart TM. Developed by IGL, it's a new way to locate inclusions in a diamond without the use of a plot. As long as the gemologist or appraiser has the chart below, he/she can communicate where the inclusions are located according to their related letter/number on the chart. For example... a feather may extend from the table to star to bezel facets at this exact location on a diamond Feather: 00-S1-B1 or Pinpoint: U8, B6, S3
inert. No detectable reaction to fluorescence.
internally flawless (IF). A clarity grade which describes a diamond without internal imperfections or flaws but with minor surface blemishes such as scratches, small naturals, etc.
irradiated diamond. A diamond that has been subjected to bombardment by fast electrons, neutrons, and deutrons in-order to change its colour to make it more attractive and desireable.
isometric system. Same as cubic system.
Jewellers Vigilance Canada - JVC. A non-profit association founded in 1987 to advance ethical practices. To promote consumer protection, publish ethical guidelines, assist law enforcement agencies and to help level the playing field in the jewellery industry.
JVC - 27 Queen Street East, Suite 600, Toronto, Ontario CANADA M5C 2M6
Toll free: 1-800-636-9536
in Toronto: (416) 368-4840
Fax: (416) 368-5552
Email: jewellers.vigilance@sympatico.ca
Jewelers' Vigilance Committee - JVC (USA). A non-profit association founded in 1912 to advance ethical practices in the jewellery trade.
jeweller. Someone who has knowledge through experience and education on selling diamonds, coloured stones, jewellery and watches plus gift ware in a retail environment. They must be well versed on the products that they are selling and servicing these products in the years to come.
K or Kt. Are abbreviations for karat.
karat. The proportion of pure gold in an alloy. Pure gold is 24 karat, 22K is 91.6% pure, 18K is 75.0% pure, 14K is 58.3% pure and 10K is 41.7% pure gold.
keel line. A line running the length of the pavilion of a fancy-shaped stone.
kimberlite. The name applied to the type of mafic igneous rock that is the host rock of diamonds in all primary diamond deposits discovered to date.
kite facets. The
eight main bezel facets, the outlines of which resemble a kite. 
knife-edge girdle. A girdle of a diamond that is so thin that it can be likened to the edge of a sharp knife (chips easily).
knot. An included crystal that is oriented differently from the host crystal & is encountered during the fashioning process. Knots stand out as small, raised surfaces after the processing operation.
Koh-i-Noor Diamond. Set in Queen Elizabeth the Queen Mother's Crown recut
to 108.93 carat oval. 
lap. A flat,horizontal, diamond dust-impregnated cast-iron wheel, 12 to 18 inches in diameter, that revolves about a vertical shaft. It is used for grinding & polishing facets on diamonds and coloured stones.
lapidary. A cutter, grinder and polisher of coloured stones.
laser. Acronym for Light Amplification by Stimulated Emission of Radiation. Laser systems have been used to enhance the clarity grade of diamonds by providing passages to dark carbon inclusions and to act as conduits for bleaching agents.
laser cut. A diamond or coloured stone cut and faceted with a laser, usually in different non-geometric shapes. However, the amount of wasted material is a lot higher than lap fashioning.
Leveridge guage. A millimeter dial micrometer designed for measuring mounted
and loose diamonds and coloured stones of various styles of cutting.
loupe. For grading diamonds, a loupe must be 10 power corrected for spherical
& chromatic aberration.
luminescence. The emission of certain wavelengths of light by a diamond or other substance when excited by radiation of different wavelengths, electrical charge, heat, or friction.
lustre. The appearance of a material's surface in reflected light, as determined by the quantity & quality of light reflected. Smoothness & R.I. are the main factors affecting lustre. Greasy lustre = rough and adamantine lustre for fashioned.
macle. A flat, triangular rough diamond, which is a twinned crystal of the spinel-twin type. It is more difficult to fashion than most other crystals because of the differing grain directions caused by the twinning. Often used for fancy shapes.
main facets. The large crown & pavilion facets of a brilliant cut diamond or other gem.
make. A term referring to the proportions and finish of a fashioned diamond.
marquise
brilliant cut. Cutting style in which the girdle outline is boat shaped.
melange. An assortment of diamonds of mixed weights &/or qualities and of sizes larger than melee.
melee. A term describing smaller diamonds weighing less than 0.20 carat, in brilliant and non-brilliant styles.
metric carat. 0.200 grams, or 200 milligrams.
microscope. See binocular microscope...
millimeter (mm). Metric system unit of length based upon the meter as a standard of measurement. 1mm = 0.001 meter.
millimeter micrometer. A precision caliper guage that measures the overall dimensions of unmounted fashioned gems accurately (to 0.01mm) but less conveniently than dial guages. The screw micrometer features a direct reading digital scale for quick, easy, accurate measurement of stones from 0.01mm to 25.50mm.
mixed cut. A faceted gem where the crown is brilliant cut and the pavilion is step cut. Sometimes the reverse is seen.
Mohs scale of hardness:
|
1.
|
Talc Comparison of Mohs relative hardness scale and absolute measurements of hardness *Diamond
is extremely hard and |
|
|
|
Consumer
Facts: - A hardness of 7 and higher is recommended for gemstones worn in jewellery. |
|
| - Gemstones with hardness greater than 5.5 can scratch glass. |
moissanite, synthetic. A man-made material with a natural counterpart that can be used as a diamond simulant. S.G. of 5.7, R.I. of 2.15, and hardness of 9.25
mounting. A piece of jewellery in which a gem is to be set in.
natural. A portion of the original surface of a rough diamond that is sometimes left by the cutter, usually on the girdle. Naturals indicate an effort to retain the maximum diameter from the original rough in the rounding-up and polishing stages.
negative crystal. An angular cavity within a crystal or fashioned gemstone. It is a rare occurence in diamond, and quite common in ruby.
nick. A minor chip out of the surface of a diamond, usually caused by a light blow. (Considered to be blemishes).
nitrogen (N). Occurs as a trace element inclusion in the lattice in some diamonds. The cause of the yellow colour in diamonds.
"north light". The traditional light source used in colour grading diamonds. Illuminated from the northern sky between 10 a.m. and 12 noon. It affords the least variation of intensity and colour, is relatively shadow free, and contains the least amount of ultraviolet.
Northwest Territories (N.W.T.). Province in Canada's north, known for it's natural resources. The new site for high quality rough diamonds at the Ekati mine with state-of-the-art sorting and cutting facilities in Yellowknife.
octahedral cleavage. Cleavage parallel to any of the four pairs of faces of the octahedron.
octahedron. One of the seven basic forms in the highest symmetry class of
the cubic crystal system. It has eight equilateral, triangular faces, each of
which intersects all three of the crystallographic axes at an equal distance
from the centre.
off-centre culet. A culet that is off centre with respect to the girdle outline, due to polisher's error.
off-centre table. Distorted rough is sometimes cut in a manner that places the table nearer to the girdle at one point than elsewhere.
old european cut. A term applied to the earliest form of circular-girdle full brilliant. It features a small table, a heavy crown and great overall depth.
old
mine cut. A term applied properly to an early form of brilliant cut with
a nearly square or cushion-shaped girdle outline.
old single cut. A simple form of brilliant cutting that has an octagonal-shaped girdle outline, a table, 8 bezel facets, 8 pavilion facets, and sometimes a culet.
open culet. A culet that is larger than necessary, eye visible. It may be
described as medium, large or very large.
out-of-round diamond. A term used to describe any brilliant or other style of round-cut that does not have a truly circular girdle outline to the eye.
oval brilliant cut.
Cutting style in which the girdle outline is elliptical. 
oxidized crystal. A diamond crystal that contains iron oxide, due to contact with the atmosphere during formation of an alluvial deposit.
parcel. A collection made up of clearly defined groups of diamonds, which is ready for sale (usually after evaluation).
pave setting. Stones are set into drilled holes and metal beads are pushed over to hold the stones. Also known as bead setting.
pavilion. That portion of a faceted gemstone below the girdle.
pavilion angle. The angle between the girdle plane and the pavilion main facets.
pavilion depth. The distance measured perpendicular from the girdle plane to the culet and read as a percentage of the girdle diameter.
pavilion facets. Those facets on any fashioned stone located on the pavilion (i.e. below the girdle), as opposed to the crown facets, which are located above the girdle.
pear-shape
brilliant cut. A cutting style having a pear-shaped girdle outline, usually
with 58 facets.
pinpoint. Any small rounded inclusion seen at 10x but not larger than an included crystal.
pipe. A vertical, cylindrical or column-like mass of rock that cooled and solidified in the neck of a volcano. When these rock masses are composed of kimberlite, they sometimes contain diamonds.
pique (P.K.). A European term for an imperfection grade, used as 1st, 2nd and 3rd pique grades (same as I1, I2, and I3 grades).
pit. An indentation on the surface of a diamond. It may be caused by a blow or by a knot being pulled out from the surface during the polishing process. A large indentation is usually called a cavity; a minor one, a nick.
plot. Plotting, or recording clarity characteristics on a diagram using conventional symbols to indicate the relative size, nature, number, colour and location of inclusions and blemishes. Three colours of ink are used on the plot diagram 1) Red for inclusions, 2) Green for blemishes and 3) Black for extra facets and settings.
Reasons for Plotting:
- a plot aids in the identification of a diamond at a future date,
- it establishes the condition of a diamond at the time of plotting, and
- it supports the clarity grade assigned to the diamond.
The Inclusion Locator Chart TM, developed by IGL, is a new way to locate inclusions in a diamond without the use of a plot. As long as the gemologist or appraiser has this chart below, he/she can communicate where the inclusions are located according to their related letter/number on the chart. For example... a feather may extend from the table to star to bezel facets at this exact location on the diamond Feather: 00-S1-B1 or Pinpoint: U8, B6, S3
point. 1) In weighing diamonds, one hundredth part of a carat, each one hundredth being called a point; e.g. a diamond weighing 0.31 carat is said to be a 31-point diamond, or a 31- pointer. 2) The sharp tip of a pear-shape or marquise diamond.
polariscope. An optical instrument used to ascertain whether a gemstone
possesses single or double refraction (uniaxial or biaxial optic signs). One
of several tests to identify a stone.
polish. The relative smoothness of a surface. A well-polished diamond shows no wheel marks or surface blemishes at 10x.
polished girdle. A girdle with a lustrous curved surface or a series of flat, polished surfaces (facets).
polishing. The reduction of a rough, irregular surface to a smooth flatness. It is used to include both lapping or blocking, and brillianteering.
polishing mark. A groove or scratch left by the polishing wheel on a facet of a diamond.
princess cut. A brilliant cutting style with a square or rectangular-shaped
girdle outline.
proportions. The major factors that determine the cutting quality on a diamond; i.e. table %, total depth %, girdle thickness, crown height,crown & pavilion angles, major and minor symmetry, culet size and even details on finish.
quality, factors that determine. The quality of a diamond can be rated only when the following factors have been analyzed: 1) carat weight, 2) colour grade, 3) clarity grade, 4) cut grade including proportions & finish.
recutting. The process of refinishing a polished stone in order to improve its clarity grade, proportions, to repair damage or to improve its overall appearance. Also used to modernize an old style cut.
red diamond. The rarest of all fancy-coloured diamonds.
reflection. The returning or rebounding of light rays which strike a surface. Angle of Reflection = Angle of Incidence.
refraction. The bending of light rays. The deflection from a straight path suffered by a ray of light as it passes from a medium of one optical density to another medium of different optical density, as from air into gemstone.
refractive index (R.I.). A measure of he amount a light ray is bent as it enters or leaves a gemstone, expressed by numerals. The higher the R.I., the greater the brilliancy. The R.I. of: - diamond = 2.417, corundum = 1.77, beryl = 1.57, quartz = 1.54, amber = 1.08
refractometer. An optical instrument for measuring the refractive index
of a gemstone. This is done with the use of R.I. liquid and the hemicylinder
(featured on the refractometer).
rhinestone. The name given to a colourless lead-glass fashioned as a diamond simulant.
rough diamond. A diamond in its natural state (uncut and unpolished).
rough girdle. If a diamond is rounded up too quickly in the fashioning process, the surface of the girdle will be irregular, pitted, or granular. This condition may also be accompanied by numerous hair-like fractures extending into the stone called bearding.
sawing. The phase of the diamond-fashioning process in which a crystal is separated by abrading or grinding a narrow slit through it, using a 3" to 5" bronze disc blade with a thickness of 0.004 of an inch.
scintillation. Reflections of light from the polished facets of a gemstone seen only if the gemstone, the light source or the observer moves.
setting. Only that portion of the mounting that actually holds the stone.
Types of settings are: bead, bezel, semi-bezel, claw, channel, gypsy (flush),
and rim.
shallow stone. A diamond with either the crown, or pavilion main facets are placed at angles much less than normal. The loss in brilliancy gives the diamond a very glassy appearance.
shapes of a diamond.
single cut. Used mostly in melee, that has a circular girdle, 17 facets including a table, eight bezel facets, and eight pavilion facets.
slightly included (SI1 or 2). A grade of relative imperfection in a diamond, which is more flawed than VS but less than Imperfect.
solitaire. A term used to refer to a ring containing a single diamond or
other gemstone.
specific gravity. The ratio of the density of any substance to that of water. See hydrostatic weighing method to determine the S.G. of gems.
spectroscope. An optical instrument for determining the absorption spectrum
of a transparent material.
spectrum. Radiant energy spread so that the component wavelengths are arranged progressively.
spread stone. A diamond cut with a large table and thin crown, in order to retain greater weight from the two sawn pieces of an octahedron. Also known as "fish eye" stones.
star
facets. The eight triangular facets that bound the table of a brilliant
cut gem between the main bezel facets.
step cut. All facets are four-sided and in steps or rows, both above and below the girdle.
stone. A trade term for a cut and polished diamond or any other natural gemstone.
synthetic diamond. Are here, soon to reach market...more to come...
synthetic moissanite. A man-made material with a natural counterpart that can be used as a diamond simulant. S.G. of 3.22, R.I. of 2.15, and hardness of 9.25
synthetic stone. A man-made stone that has the same chemical, physical & structural properties as its natural counterpart.
table. The large
facet that caps the crown of a faceted diamond or other gemstone. 
table
down. A term used to designate a position of a diamond when grading for
colour.
tapered baguette cut. A tapered modification of the standard baguette.
thick crown. A crown thickness that is noticeably deeper than the ideal 16.2%
Tolkowsky's "ideal cut". Those proportions & facet angles that were calculated mathematically to produce maximum brilliancy consistent with a high degree of fire in a round brilliant cut diamond. These figures, computed as a percentage of the girdle diameter are: table = 53%, total depth = 59.3%, girdle thickness = 0.7 to 1.7%, crown height = 16.2%, pavilion depth = 43.1%, crown angle = 34.5 degrees, and pavilion angle = 40.5 degrees Diamond cutters who emphasize proportions consider 57% table as optimum and up to 60% as acceptable.
toughness. The resistance to breakage in a substance. In diamond, it is exceptionally tough, even along a cleavage direction, its toughness is classed as good. Toughest gem=jade
treated (enhanced) diamond. A diamond that has been coated, filled, laser drilled or otherwise treated to improve or change its colour or appearance.
trigon. A triangular marking occurring as a growth mark on diamond octahedron
faces.
trilliant cut. A cutting style with the girdle outline being triangular-shaped (with rounded sides).
triplet. An assembled stone of two parts bound together by a layer of cement which can be coloured to reproduce the colour of the stone it imitates.
twinning lines. Visible lines on or within a fashioned diamond, caused by twinning in the crystal.
ultraviolet. That portion of the spectrum just shorter than visible light
in wavelength. It is important in the study of diamond and coloured stone, because
ultraviolet radiation excites some of the fluorescent effects seen in some diamonds.
upper girdle facets.
very slightly included (VS1 or 2).
very, very slightly included (VVS1 or 2).
visible light spectrum. Red - Orange - Yellow - Green - Blue - Violet - Purple
wing. The tapered area at each end of a marquise leading from the belly. Also occurs in pear and heart shape.
X-ray fluorescence. Gem diamonds fluoresce when exposed to X-rays. The fluorescence usually shows varying intensities of blue. Other colours are seen, but the intensity is weaker.
yellow diamond. A diamond with a yellow body colour. The tone of the colour may be exceedingly light to very pronounced.
yellow ground. Weathered blue ground. See blue ground, or kimberlite.
Yellowknife. Up and coming Canadian sorting and cutting centre in N.W.T.
zirconia, cubic (CZ). A man-made material (comes in several colours) without a natural counterpart that can be used as a diamond simulant. S.G. of 5.7, R.I. of 2.15, and hardness of 8.5
GIA's Diamond Colour Grading Scale
D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V |
W | X | Y | Z
colorless ......................................................................................fancy
yellow
GIA's Fancy Colour
Grading Scale
D to Z - FANCY LIGHT - FANCY INTENSE - FANCY VIVID - FANCY DARK - FANCY DEEP
* Diamonds are graded face-up for body colour other than yellow & brown.
GIA's Diamond Clarity
Grading Scale
Fl - Flawless
IF - Internally flawless
VVS1 - Very, very slightly included - 1
VVS2 - Very, very slightly included - 2
VS1 - Very slightly included - 1
VS2 - Very slightly included - 2
SI1 - Slightly included - 1
SI2 - Slightly included - 2
I1 - Imperfect - 1 (1st Pique)
I2 - Imperfect - 2 (2nd Pique)
I3 - Imperfect - 3 (3rd Pique)
GIA's Diamond Cut
Grading Scale | IGL's Diamond Cut Grading Scale
Class 1 A , B ................................... Ideal, Very Good
Class 2 A , B ................................... Good, Medium-Good
Class 3 A , B ................................... Medium, Fair-Medium
Class 4 A , B ................................... Fair, Poor
 |
|
| January | Garnet |
| February | Amethyst |
| March | Aquamarine, Bloodstone |
| April | Diamond |
| May | Emerald |
| June | Pearl, Opal, Alexandrite |
| July | Ruby |
| August | Peridot |
| September | Sapphire |
| October | Tourmaline |
| November | Topaz |
| December | Zircon, Turquoise |
