A complete glossary of diamond terminology, covering the 4Cs, cuts, certificates, optical phenomena, inclusion types, jewelry settings and market terms. Entries prepared by Marta Kłosowska, Diament Expert specialist.
A
AGS (American Gem Society)
An American gemological organization that issues diamond reports and its own precise cut grading scale (0–10), less common in Europe than GIA or IGI but respected for its exacting evaluation of proportions.
AGS Ideal Cut
The highest cut grade in the American Gem Society system, which considers both proportions and how the stone returns and disperses light.
AML / KYC
Anti-Money Laundering and Know Your Customer procedures that verify the identity of buyers and the legitimacy of funds, required for high-value purchases such as investment diamonds.
Appraisal
An independent valuation of a diamond or jewelry piece, usually prepared for insurance. Unlike a grading report, it states a specific monetary value at a given time and place.
ASET (Angular Spectrum Evaluation Tool)
A gemological tool that maps how light is returned by a diamond, showing areas of light return and light leakage. It helps assess cut quality, especially in round brilliants.
Asscher Cut
A square step cut with cropped corners and deep, stair-like facets that create a "hall of mirrors" effect rather than the sparkle of a brilliant.
Authenticity
Confirmation that a stone is a genuine diamond (natural or lab-grown) and not an imitation such as cubic zirconia or moissanite. It is verified through the grading report and the laser inscription number on the girdle.
Authorized Dealer
A seller verified by payment institutions and holding full financial and legal documentation (KYC/AML), as opposed to anonymous sales platforms with no history.
B
Baguette Cut
A narrow, rectangular step cut without cropped corners, used almost exclusively as a side stone in channel settings.
Bearding
Tiny, whisker-like fissures along the girdle edge, caused during cutting. Minor bearding is harmless and can often be removed by repolishing.
Bezel Setting
A setting in which the diamond is surrounded by a metal rim instead of individual prongs. It protects the stone well, at the cost of slightly less light entering from the sides.
Black Inclusion
A dark inclusion inside a diamond or near its surface, which may appear as a small spot, crystal or other structure visible under magnification. Its significance depends on size, position, contrast and effect on overall clarity. Not every black inclusion is visible to the naked eye.
Blemish
An imperfection on the outer surface of a diamond, as opposed to an inclusion, which lies inside the stone.
Blood Diamond (Conflict Diamond)
A diamond mined in a war zone and sold to finance armed conflict, with no legitimate supply chain. Trade is regulated by the Kimberley Process.
Bow Tie
A dark, bow-tie-shaped shadow across the center of elongated shapes (oval, marquise, pear, elongated cushion), caused by improper cut proportions. The less visible it is, the better the cut.
Bracelet
A bracelet with set diamonds, most often a tennis bracelet (identical stones in a line) or a single accent on a chain.
Brilliance
The amount of white light reflected toward the viewer's eye, determined mainly by cut quality.
Brilliant Cut (Round Brilliant)
The most popular diamond cut: round, typically with 57–58 facets, and the benchmark for all other shapes.
Bruise
A small surface damage made of tiny fractures, usually caused by impact. Classified as a blemish, not an inclusion.
Bruting
The stage of processing rough diamond in which it is given a preliminary round shape by friction against another diamond, before the facets are cut.
C
Carat
The unit of diamond weight; 1 carat (1 ct) equals 0.2 grams. One of the 4Cs.
Carbon
The chemical element diamond is made of; its atoms form a regular cubic crystal lattice responsible for the stone's exceptional hardness.
Cavity
A hollow or small loss on the surface of a diamond, graded as a clarity characteristic. It can form where a crystal fell out during cutting.
Certificate (Grading Report)
A document from an independent laboratory (GIA, IGI, HRD) describing all of a diamond's parameters, with a unique number often laser-inscribed on the girdle.
Channel Setting
A setting in which stones sit in a groove between two metal strips with no visible prongs, creating a smooth, continuous line of sparkle.
Chip
A small loss of material on the diamond's surface, usually at the girdle or a corner, caused by impact.
Clarity
An assessment of the number, size and visibility of internal inclusions and external blemishes, on a scale from FL (Flawless) to I (Included).
Clarity Characteristics
Internal and external features of a diamond that influence its clarity grade. They include inclusions such as crystals and feathers, and surface blemishes such as scratches or natural growth marks. Their type, size, number, position and visibility all matter when determining the grade.
Clarity Plot
A graphic representation of a diamond's clarity characteristics on the grading report. It shows the approximate position of characteristic inclusions and blemishes such as crystals, feathers or clouds. It helps explain the clarity grade, but it is not a photograph of the stone's interior or an exact map of every inclusion.
Cleaving
The traditional method of splitting rough diamond along its natural cleavage planes, today largely replaced by precise laser sawing.
Cloud
A cluster of tiny inclusions too small to separate, forming a hazy area inside the diamond, usually visible only under magnification.
Cluster Ring
A ring in which several smaller diamonds are grouped to visually create the impression of one larger stone.
Color
One of the 4Cs, graded from D (colorless) to Z (noticeable yellow tint). The closer to D, the less color the stone shows.
Color Grading
The process of determining a diamond's color grade on an accepted gemological scale. For typical colorless and near-colorless diamonds, the D–Z scale is used. Grading is done under controlled conditions, because lighting, surroundings and viewing method can affect how color is perceived.
Color Zoning
An uneven distribution of color in a diamond. In some stones the color may be more intense in certain areas and weaker in others. It is particularly important when assessing fancy color diamonds because it affects their appearance and attractiveness after cutting.
Crown
The upper part of a cut diamond, above the girdle up to the table. Its angles and facets control the play of light seen from above.
Crown Angle
The angle of the crown facets relative to the girdle. It affects how light is refracted and reflected, and therefore the brightness, fire and overall look of the brilliant. It should be analyzed together with the other proportions, as a single value does not decide cut quality.
Crown Height
The height of the upper part of the diamond, measured from the girdle to the table, usually given as a percentage of the stone's diameter. It affects the proportions of the brilliant and how light is dispersed, so it matters when judging cut quality.
Crystal
An inclusion type: a microscopic crystal of another mineral trapped inside the diamond as it formed.
Cubic Zirconia
A synthetic mineral used as an inexpensive diamond imitation. Its density, hardness and refractive index differ from diamond, so a diamond tester easily tells them apart.
Culet
The smallest facet at the very bottom of the pavilion. In modern cuts it is usually invisible; an oversized culet causes loss of brilliance.
Cushion Cut
A square or rectangular cut with rounded corners, valued for its soft sparkle.
Cut
One of the 4Cs, describing the quality of a diamond's proportions, symmetry and polish. It determines how much light the stone returns.
Cut Grade
An overall grade of cut quality from Excellent to Poor, taking proportions, symmetry and polish together. The single most important indicator of how much a stone will sparkle.
CVD (Chemical Vapor Deposition)
One of two main methods of producing lab-grown diamonds, in which carbon atoms are deposited layer by layer in a vacuum chamber.
D
Density
Diamond has a density of about 3.52 g/cm³, which helps distinguish real diamond from imitations such as cubic zirconia.
Depth
The height of a diamond from table to culet, expressed as a percentage of its diameter. Non-ideal depth causes light leakage and loss of brilliance.
Depth Percentage
The ratio of the diamond's total height to its diameter or width, expressed as a percentage. For a round brilliant it helps show whether the stone is too shallow or too deep, and should be read together with the other proportions and the optical assessment of the cut.
Diameter
The distance between opposite points of the diamond's outline. For a round brilliant a range of measurements is usually given. Diameter shows the real size of the stone seen from above and allows comparison of diamonds of the same weight but different proportions.
Diamond 4C
The international system for describing diamonds, based on four criteria: Carat (weight), Color, Clarity and Cut. It allows stones to be compared by unified rules. In practice, proportions, fluorescence, workmanship and individual features also affect a diamond's appearance and value.
Diamond Bourse
An organized wholesale market where rough and polished diamonds are traded between industry companies, such as the one in Antwerp.
Diamond Concierge
A personal advisory service that helps clients choose a diamond with the support of an expert.
Diamond Dossier
A simplified GIA report issued for smaller diamonds (under about 1 carat), listing the same key parameters as the full Diamond Grading Report.
Diamond Dust
A fine diamond powder produced when cutting and polishing stones, used industrially as an abrasive.
Diamond Fund
A form of investing in diamonds through a collective investment fund instead of buying a single stone directly.
Diamond Grading Report
A report issued by a gemological laboratory evaluating a diamond's main parameters. It may include weight, color, clarity, cut quality, proportions, polish, symmetry and fluorescence. It helps verify the stone's properties and compare it with other diamonds of similar parameters.
Diamond Index
A summary of average diamond prices on the global market over a given period, used by investors to track value trends.
Diamond Proportions
The mutual dimensions and angles of the parts of a diamond, such as crown height, pavilion depth, table diameter and girdle thickness. Proportions influence how light behaves inside the stone. Evaluating them requires analyzing several parameters at once, not just one value.
Dispersion
The splitting of white light into spectral colors as it passes through a diamond, responsible for the rainbow flashes known as "fire."
E
Earrings
Jewelry with diamonds worn on the ears, most often sold in matched pairs of similar weight and parameters.
EGL (European Gemological Laboratory)
A network of gemological labs issuing diamond reports. Its grades are often considered less strict than GIA or AGS, so always verify the report number on the issuing lab's website.
Elongated Cushion
A cushion cut with elongated rather than nearly square proportions, optically lengthening the finger like an oval or marquise.
Emerald Cut
A rectangular step cut with parallel, stair-like facets that produce a "hall of mirrors" effect.
Engagement Ring
A ring symbolizing engagement, traditionally set with a diamond, most often in a solitaire or halo setting.
Etch Channel
A very fine natural channel formed as the diamond crystal grew, visible only under high magnification and classified as an inclusion.
Eternity Ring
A ring with diamonds set around the entire band, symbolizing infinity, as opposed to a "half eternity" ring where stones cover only half.
Excellent Cut
The highest cut grade on the scale used by GIA, among others, for round brilliants. It means the assessed cut parameters fall within the range for that class. When choosing a diamond it is still worth viewing the real stone on video and checking proportions and light behavior.
Extinction
Dark areas in a diamond where light is not returned to the viewer's eye, related to cut proportions and angles.
Extra Facet
An additional, non-standard facet added during cutting, usually to remove a visible blemish or inclusion near the surface.
Extremely Thin Girdle
A very thin girdle, the edge separating the crown from the pavilion. Such a finish can make the stone more prone to mechanical damage, especially during setting and daily wear. Besides girdle thickness, check its evenness and the stone's overall construction.
Eye Clean
A diamond whose inclusions are not visible to the naked eye at a normal viewing distance, regardless of its formal clarity grade. Commonly used when evaluating SI1/SI2 stones.
Eye Visible Inclusions
Inclusions that can be seen without a loupe or microscope under certain viewing conditions. Visibility depends on size, contrast, position and lighting. Two diamonds with the same clarity grade can look very different, so check the stone in magnified photos and video before buying.
F
Facet
A single flat, polished surface of a diamond. The number, shape and arrangement of facets determine how the stone reflects and disperses light.
Faint Fluorescence
A weak reaction of the diamond to ultraviolet light. It can be hard to notice in ordinary lighting and usually does not significantly affect everyday appearance. Fluorescence information is given in the grading report.
Fancy Blue
A diamond of natural blue color, usually caused by trace boron in its crystal structure. One of the rarer and most valued fancy colors.
Fancy Color Diamond
A diamond with an intense natural color beyond the D–Z scale, such as yellow, pink, blue, green or black, graded on a separate color intensity scale.
Fancy Green
A diamond of natural green color, caused by natural irradiation in the Earth's crust. One of the rarest fancy colors.
Fancy Pink
A diamond of natural pink color, caused by distortions in the crystal structure rather than an added element.
Fancy Shape
A collective term for all cuts other than the round brilliant, such as oval, cushion, pear, emerald, marquise or heart.
Fancy Yellow
A diamond of natural intense yellow color, caused by nitrogen in the crystal structure. One of the more available fancy colors.
Feather
An internal fracture in a diamond, named for its feathery appearance under magnification.
Fire
The colorful flashes produced when white light is dispersed within a diamond, visible as the stone or viewer moves.
Fisheye Effect
An optical effect seen in too-shallow princess or radiant cuts: a bright circular ring in the center of the stone that reduces brilliance.
FL (Flawless)
The highest clarity grade: no inclusions or blemishes visible under 10x magnification.
Fluorescence
A diamond's emission of visible light (usually blue) under ultraviolet radiation, graded from None to Very Strong. It does not automatically mean lower quality.
Fluorescence Color
The color of light a diamond emits under ultraviolet radiation. Blue is the most common, but other colors can occur. It is separate from fluorescence intensity and may be noted in the grading report.
Fluorescence Intensity
The strength of a diamond's reaction to ultraviolet light. Reports use terms such as None, Faint, Medium, Strong and Very Strong. Intensity is not the same as the diamond's color and does not by itself determine quality or value.
Fracture Filling
A treatment that fills visible fractures with a substance of similar refractive index, reducing their visibility. It must be disclosed on the report.
Full Cut
A diamond cut with the full 57–58 brilliant facets, as opposed to the simplified single cut used on very small stones.
G
GCAL (Gem Certification & Assurance Lab)
An American gemological laboratory known for its online verification system and for reports accompanying some diamonds sold with resale guarantees.
Gemological Report
A document prepared by a gemological laboratory describing the properties of a gemstone. For a diamond it can include weight, color, clarity, cut, proportions and fluorescence. It helps identify the stone and verify its parameters before purchase.
Gemology
The science of studying gemstones: their structure, optical properties, origin and identification methods.
Gemstones
A broad category of minerals valued for beauty, durability and rarity. Besides diamond it includes ruby, sapphire and emerald.
GIA (Gemological Institute of America)
One of the world's most respected gemological laboratories and the creator of the widely used 4Cs system.
Girdle
The narrow band around the diamond's edge separating the crown from the pavilion. Laboratories laser-inscribe the report number here.
Girdle Thickness
A grade from Extremely Thin to Extremely Thick. Too thin raises the risk of chipping; too thick adds weight without adding visible size.
Graining
Structural features of a diamond related to its natural growth and crystal arrangement. They may appear as delicate lines, bands or areas of different structure, sometimes visible only under magnification. Their significance depends on type, intensity and effect on transparency.
H
Half-Moon Cut
A rare fancy cut shaped like half a circle, usually used as side stones in symmetrical pairs.
Halo
A setting in which the center diamond is surrounded by a ring of smaller stones, optically enlarging the main stone.
Hardness
Diamond is the hardest naturally occurring mineral on Earth, rated 10 on the Mohs scale and resistant to everyday scratching.
HCA (Holloway Cut Advisor)
A tool for preliminary analysis of a round brilliant's proportions, using table, depth and crown and pavilion angles, among others. It can help rule out stones with less favorable proportions, but it does not replace inspecting the diamond or a professional assessment of cut quality.
Heart Cut
A heart-shaped cut that requires precision to keep both halves symmetrical.
Hearts and Arrows
An optical pattern seen in precisely cut round brilliants with ideal symmetry: arrows when viewed from above through a special viewer, hearts from below. A sign of superior cutting craftsmanship.
Hearts and Arrows Viewer
A device or optical system that allows observation of the characteristic hearts and arrows pattern in a suitably cut round brilliant. The symmetrical pattern is linked to facet precision. It can indicate a high level of craftsmanship, but the name alone does not replace a full assessment of the diamond's parameters.
HPHT (High Pressure High Temperature)
A lab-grown diamond production method that imitates natural conditions, also used as a color-enhancement treatment for natural diamonds.
HRD (Hoge Raad voor Diamant)
A Belgian gemological laboratory based in Antwerp, one of the three most widely recognized alongside GIA and IGI.
Hue
The basic shade of a diamond's color. In fancy color stones it can describe, for example, a yellow, pink, blue or green character. Hue should be distinguished from saturation and tone, as all these together shape the final appearance and grade of a colored diamond.
I
I1 / I2 / I3
The lowest clarity grades (Included): inclusions are visible to the naked eye, especially in I2 and I3, which significantly lowers the price.
Ideal Cut
A term used for diamonds with very favorable proportions and high cut quality. There is no single universal definition for all shapes and grading systems, so check which standard the grade was assigned under and how the diamond actually looks.
IF (Internally Flawless)
The second-highest clarity grade: no internal inclusions visible under 10x magnification.
IGI (International Gemological Institute)
One of the world's largest independent gemological laboratories, especially prominent in certifying lab-grown diamonds.
Inclusion
An internal feature of a diamond (such as a crystal, feather or cloud) formed naturally during its growth. The number and visibility of inclusions determine the clarity grade.
Inclusion Location
The position of an inclusion in a diamond: in the center, near the girdle, under the table or close to the surface. Location affects visibility, appearance and potential effect on durability, so look at the placement of internal features and not only the clarity grade.
Inclusion Plot
A diagram showing the position of inclusions and other clarity characteristics in a diamond, included in many grading reports. It is indicative and does not show the exact appearance or real scale of each inclusion.
Indented Natural
A part of the original rough surface left below the girdle level on purpose to avoid losing more weight during cutting.
Industrial Diamonds
Natural or synthetic diamonds that do not meet jewelry standards, used in industry for cutting and abrasive tools because of their hardness.
Insurance
A policy protecting against loss, theft or damage of a diamond and its setting, usually requiring an independent appraisal and the stone's report.
Internal Graining
Faint lines or streaks inside a diamond formed during growth. They do not usually affect durability but are considered in clarity grading.
Investment Diamond
A diamond of high clarity and color, typically from about 1 carat upward, purchased as a store of value.
J
Jeweler
A specialist who designs, makes or appraises jewelry and gemstones.
K
Kimberley Process
An international certification scheme designed to prevent trade in conflict diamonds by requiring documentation of origin for rough diamonds.
Kimberlite
The igneous rock that is the main source of natural diamonds, carried from deep within the Earth to the surface through kimberlite pipes.
Kite Cut
A rare four-sided fancy cut shaped like a kite, used mainly as an accent stone.
Knot
An inclusion that is a crystal of another mineral reaching the diamond's surface, visible as a small bump.
L
Lab-Grown Diamond
A diamond created by CVD or HPHT in controlled conditions, with the same physical and optical properties as a natural diamond.
Laser Drill Hole
A microscopic channel drilled by laser to reach a dark inclusion and lighten or remove it. A treatment that must be disclosed on the report.
Laser Inscription
The report number engraved by laser on the girdle, visible under a loupe, allowing the stone to be matched to its report.
Light Return
The amount of light entering the diamond and reflected back to the viewer's eye, a key indicator of cut quality.
Liquidity
How easily an investment diamond can be sold at a price close to market value, depending on demand for its parameters.
Lonsdaleite
A rare hexagonal form of diamond, formed for example at meteorite impact sites, with no jewelry use.
Loose Diamond
A diamond not set in jewelry, sold on its own with a report, for example to design a custom ring.
Loupe (Jeweler's Loupe)
A magnifying tool (usually 10x) used by gemologists and jewelers to grade clarity and read the girdle inscription.
M
Marquise Cut
An elongated cut with pointed ends, resembling a boat, which makes the finger appear longer.
Matched Pair
Two diamonds with very similar weight, color, clarity and cut, sold together, mainly for earrings.
Melee
Small diamonds, usually under 0.18 ct, used as accent stones in halo, pavé or channel settings.
Metal Setting
The metal in which the diamond is set, usually white, yellow or rose gold (in various purities) or platinum, differing in color, durability and price.
Milky Appearance
A visual effect of milky haze visible in a diamond. It can make the stone look less transparent and its reflections weaker or less distinct. It should not automatically be equated with fluorescence, as the causes of a milky look can differ.
Milky Diamond
A diamond with a milky, hazy look, which may result from numerous tiny inclusions, light scattering or other internal features. Such a stone may have limited transparency and less distinct brilliance. Judge the degree of haze from video and photos in different lighting.
Mixed Cut
A cut that combines brilliant facets on the crown with step facets on the pavilion, or vice versa.
Modified Brilliant Cut
A variation of the brilliant cut in which the arrangement or number of facets differs from the classic pattern, used in various diamond shapes to achieve a particular visual effect. Some fancy shapes combine classic brilliant features with extra modifications.
Mohs Scale
A ten-point mineral hardness scale on which diamond ranks highest, at 10.
Moissanite
A very rare natural mineral, now produced synthetically, used as a diamond simulant. It has higher dispersion than diamond, which helps tell them apart.
N
Natural Diamond
A diamond formed in nature deep inside the Earth under immense pressure and heat over millions of years.
Natural (Girdle Feature)
A portion of the original, unpolished surface of the rough diamond left on the girdle of the finished stone to minimize weight loss during cutting.
Necklace
A piece of jewelry worn around the neck, in which a diamond may be a single accent (pendant) or part of a larger composition.
O
Old European Cut
An antique round cut used from the late 19th to the mid-20th century, a predecessor of the modern brilliant, with a larger culet and fewer facets that give a warm, flickering sparkle.
Old Mine Cut
An early antique cut with a cushion-like, irregular outline and hand-cut facets, found mainly in antique jewelry from before the 20th century.
Optical Performance
How a diamond responds to light and how it looks when observed, including brightness, fire, contrast and scintillation. It is influenced by proportions, cut precision, facet symmetry and lighting, and helps in understanding the stone's real appearance.
Optical Symmetry
The degree of order and evenness of the optical pattern created by a diamond's facets. High symmetry can favor regular reflections and characteristic light patterns. It should be distinguished from the Symmetry Grade, which is one of the parameters in a grading report.
Oval Cut
An elongated brilliant cut combining classic sparkle with a finger-lengthening effect.
Oval Ratio
The length-to-width ratio of an oval-cut diamond, showing whether the stone is more slender or more rounded. The choice is aesthetic, but it also affects how the diamond looks in jewelry and how much it lengthens the finger in a ring.
P
Pavé Setting
A setting in which many very small diamonds are set close together, creating a "paved" surface of sparkle.
Pavilion
The lower part of a cut diamond, below the girdle. Its angles determine whether light is reflected back upward.
Pavilion Angle
The angle of the facets of the lower part of the diamond, below the girdle. It affects how light reflects inside the stone and returns through the crown. It should be analyzed together with the crown angle and other proportions, as their match is important for the brilliant's optical quality.
Pavilion Depth
The depth of the lower part of the diamond, measured from the girdle to the culet, often given as a percentage of the diameter. It affects the path of light inside the stone and should be judged together with the other proportions.
Pear Cut
A teardrop-shaped cut combining features of the round brilliant and the marquise.
Pendant
A piece of jewelry with a single diamond hanging on a chain, worn as the centerpiece of the ornament.
Pinpoint
A very small, dot-like inclusion, usually a tiny crystal, hard to see even under magnification. Common in VVS grades.
Pit
A microscopic cavity on the diamond's surface, classified as a blemish and usually invisible to the naked eye.
Point
A unit of weight equal to 0.01 carat; a 0.75 ct diamond can also be described as "75 points."
Polish
A grade of the surface smoothness of the facets after cutting. Poor polish reduces the light reflected.
Polish Grade
A grade of the surface finish of a diamond after cutting and polishing. It indicates whether facets show polishing marks, unevenness or other surface imperfections. Reports use grades from Excellent to Poor. High polish quality helps achieve smooth facet surfaces.
Portuguese Cut
A cut with an extra layer of facets that increases brilliance, especially in larger stones.
Precision of Cut
The accuracy of each facet and their mutual arrangement. High precision can favor a regular pattern of reflections and a harmonious look. It is broader than the proportions grade alone, as it includes the quality and accuracy of the cutting work.
Price per Carat
A pricing method in which price rises non-linearly with weight; stones of "round" weights such as 1.00 ct cost proportionally more than 0.90 ct.
Princess Cut
A square cut with sharp corners and many facets, offering brilliance close to a round diamond in a modern, geometric shape.
Prong Setting
The most popular setting, in which metal prongs (usually 4 or 6) hold the diamond, maximizing the light reaching the stone.
Proportion Diagram
A graphic representation of a diamond's dimensions and proportions, often included in the grading report. It may show depth percentage, table size, girdle thickness and crown and pavilion angles, and helps analyze the stone's construction and compare diamonds of similar weight.
Proportions
The ratio of a diamond's dimensions (depth, table, crown and pavilion angles) to its diameter, which determines how well it reflects light regardless of carat weight.
Proportions Grade
An assessment of a diamond's proportions: the relationships between its dimensions and angles. Depending on the lab, it may be a separate classification or part of the overall cut grade. Proportions matter for appearance but should not be analyzed apart from the stone's real light behavior.
R
Radiant Cut
A rectangular or square cut with cropped corners, combining the geometric outline of the emerald cut with the sparkle of a brilliant.
Rapaport (Rap List)
A weekly list of reference wholesale diamond prices, widely used as a benchmark in trade negotiations, although retail prices can differ significantly.
Refractive Index
Diamond has one of the highest refractive indices among natural minerals (about 2.42), which gives it its characteristic brilliance.
Report Check
An online service offered by laboratories (GIA, IGI, HRD) that verifies a report's authenticity from its number, to be compared with the stone's description and girdle inscription.
Resale Value
The amount obtainable when selling a diamond again. It is usually lower than the retail purchase price, though high-quality investment diamonds hold value better.
Rose Cut
An antique cut with a flat base and a domed top covered in triangular facets, without a table or pavilion, giving a soft glow rather than intense sparkle.
Rough Diamond
A diamond in its as-mined state, before cutting and polishing.
S
Scintillation
The sparkle of alternating flashes of light and dark areas seen as the diamond, the viewer or the light source moves.
Second-Hand Diamond
A previously owned diamond sold again. Its resale value depends on current market prices, the report and the stone's condition, not on its original price.
Setting
The way a diamond is mounted in jewelry, such as prong, bezel, halo or channel, affecting stone security and how much light reaches it.
Shank
The band of a ring that encircles the finger and connects to the setting of the center stone.
SI1 (Slightly Included 1)
A clarity grade in which inclusions are visible under magnification but usually not to the naked eye.
SI2 (Slightly Included 2)
A clarity grade slightly below SI1, where inclusions may sometimes be visible to the naked eye.
Side Stones
Smaller diamonds set beside the center stone, for example in a three-stone ring or as accents on a solitaire.
Signet Ring
A massive ring with a flat or domed surface, traditionally worn as a sign of status or family, increasingly set with a single diamond.
Single Cut
A simplified cut with 17–18 facets instead of 57–58, used almost exclusively on very small diamonds (melee).
Solitaire
A classic setting in which a single diamond is set alone, without side stones, usually in a prong setting.
Split Shank
A ring shank that divides into two bands as it approaches the center stone, giving a light look and extra space for small stones.
Spread
How large a diamond looks from above relative to its carat weight. Two stones of identical weight can have different diameters and seem larger or smaller. Spread depends mainly on proportions and depth, so compare dimensions in millimeters.
Star Facets
Small triangular facets on the crown around the table; lower girdle facets are on the pavilion near the girdle. Their precision affects scintillation.
Strong Fluorescence
A strong reaction of the diamond to ultraviolet light, most often a blue glow, though other colors are possible. Its effect on appearance depends on the particular stone and does not automatically mean lower quality, so evaluate the diamond in daylight and typical lighting.
Surface Graining
Features of the crystal structure that may show on or near the diamond's surface. They can affect appearance and grade depending on intensity and visibility. Proper interpretation requires magnification and reference to the description in the grading report.
Symmetry
A grade of how precisely the facets are aligned and matched, affecting how efficiently the diamond reflects light.
Symmetry Grade
A grade of the symmetry of a diamond's execution, considering the placement, shape and mutual fit of facets. In reports it may range from Excellent to Poor. Good symmetry helps give the stone an orderly look, but the grade alone does not define the total quality of the cut.
Synthetic Diamond
Another name for a lab-grown diamond, although trade more often uses "lab-grown" to avoid association with cheap imitations.
T
Table
The largest flat facet on top of the diamond, through which most of the visible light enters and exits.
Tension Setting
A modern setting in which the diamond is held only by the tension of the metal on both sides, so it appears suspended in air.
Three-Stone Ring
A ring with one larger center diamond and two smaller ones at the sides, often said to represent the past, present and future of a relationship.
Toi et Moi Ring
A ring with two stones set side by side, usually of different color or shape, symbolizing two people.
Total Carat Weight (TCW)
The combined weight of all diamonds in a piece of jewelry (center and accent stones), usually given next to the weight of the main stone.
Trapezoid Cut
A trapezoid-shaped cut used mainly as a side stone beside a larger center stone.
Treatment
Any process that improves a diamond's appearance, such as irradiation, fracture filling or HPHT. Treatments should be disclosed on the report.
Trellis Setting
A setting in which the prongs of the center stone visually interweave with those of the side stones, forming a metal lattice.
Trillion Cut
A triangular cut with sharp corners, used both as a center and as a side stone (often with cropped corners).
Twinning Wisp
An inclusion in the form of thin whitish streaks formed where two crystals grew together during the diamond's formation.
Type IIa Diamond
A rare chemical type of diamond, practically free of nitrogen, with exceptional colorlessness and optical purity. About 1–2% of natural diamonds.
U
Ultraviolet (UV)
Radiation used by gemologists to check diamond fluorescence; under a UV lamp, a strongly fluorescent stone glows, usually blue.
V
Valuation
The process of determining a diamond's market value based on the 4Cs, its report and current market prices.
VS1 (Very Slightly Included 1)
A clarity grade in which minor inclusions are hard to see with the naked eye, a popular balance of quality and price.
VS2 (Very Slightly Included 2)
Similar to VS1, with slightly larger inclusions that are still usually invisible to the naked eye.
VVS1 (Very Very Slightly Included 1)
A very high clarity grade, with inclusions extremely difficult to see even for an experienced gemologist.
VVS2 (Very Very Slightly Included 2)
A clarity grade slightly below VVS1, still considered very high.
W
Wedding Band
A wedding ring with diamonds set in it, often an eternity ring (stones around the whole band) or half eternity (stones on half of it).
Wholesale Diamond Dealer
A seller of diamonds directly, bypassing jewelry store chain margins, which allows stones of the same parameters at lower prices.
Windowing
An optical effect in which you can see through the diamond like a window, instead of seeing sparkle, caused by a cut that is too shallow.
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