The Azena Gems
Gemology Glossary

The universal framework for evaluating diamond quality, established by the Gemological Institute of America (GIA). The 4Cs stand for Cut, Color, Clarity, and Carat weight. Together they determine a diamond's appearance, rarity, and market value. The system is now used by every major grading laboratory worldwide and gives buyers a common language when comparing stones.

The 4Cs were developed by GIA founder Robert M. Shipley in the 1940s and later systematised by Richard T. Liddicoat. Before their adoption, diamond quality was described inconsistently — 'river white' or 'fine white' meant different things to different traders. Today the 4Cs underpin every grading report from GIA, IGI, HRD, and GCAL.

A square step-cut diamond with deeply cropped corners, high crown, small table, and deep pavilion, creating a distinctive 'hall of mirrors' optical effect. Developed by Joseph Asscher of Amsterdam in 1902, the original Asscher cut has 58 facets. The Royal Asscher Cut, trademarked by the Asscher family, features 74 facets for improved brilliance.

The cropped corners prevent chipping and give the stone an octagonal outline. Clarity is especially visible in step cuts; VS2 or better is recommended for asscher cuts over 1.00 ct.

A jewellery setting style in which a continuous metal rim (the bezel) is formed around the entire girdle of a gemstone, securing it by folding the metal edge over the stone's crown edge. Bezel settings offer excellent protection for the gemstone, making them ideal for active wearers or fragile stones. Full bezels surround the stone completely; half-bezels frame only two sides.

Bezel settings cover more of the gemstone than prong settings, which can slightly reduce apparent size and light entry from the sides. They offer a sleek, contemporary aesthetic popular in modern minimalist jewellery.

Any surface (external) characteristic on a finished diamond, as opposed to internal inclusions. Blemishes include scratches, nicks, chips, abrasion, naturals (unpolished rough diamond surface left on the girdle), polish lines, and extra facets. Minor blemishes appear on grading reports plotted in green to distinguish them from inclusions plotted in red.

Many blemishes occur during cutting and polishing rather than in nature. A 'natural' (preserved section of the rough diamond's original crystal surface on the girdle) is technically a blemish but is considered desirable by some as proof the diamond was cut from genuine rough.

The total amount of white light — both internal and external — reflected back to the viewer's eye from a diamond. Brilliance is the primary visual quality that makes a diamond appear bright and lively. It is determined almost entirely by the quality of the cut: well-angled facets capture incoming light, bounce it internally, and return it through the table and crown.

GIA distinguishes between external brilliance (light reflected from the diamond's outer surfaces, like a mirror) and internal brilliance (light that enters the stone, bounces off the pavilion facets, and exits through the crown). Poorly proportioned stones lose light through the pavilion or crown, appearing dark or 'dead'.

A skilled craftsperson specialising in the final stage of cutting a round brilliant diamond — polishing the star facets, upper and lower girdle facets, and ensuring all facets meet precisely at their junctions. Modern automated machines have taken over many steps, but hand-brillianteering remains valued for exceptional stones.

The term derives from the fact that these final facets create the 'brilliant' — the completed, fully-faceted stone. A master brillianteer can make the difference between a Very Good and an Excellent cut grade. The craft is concentrated in Antwerp, Surat, and Tel Aviv.

The process of shaping a diamond's girdle into a circular form by spinning two diamonds against each other on a horizontal lathe, using one to abrade the other. Since only diamond can scratch diamond, this is the primary method for rounding rough stones before faceting. Modern systems use laser-assisted bruting for precision.

Bruting produces a characteristic granular girdle surface texture unless subsequently polished. On GIA reports, girdle texture is described from Extremely Thin to Extremely Thick, with Very Thin to Slightly Thick considered ideal.

A gemstone cut to precise, standardised dimensions so that it fits pre-manufactured jewellery settings without custom adjustment. Common calibrated sizes for round stones include 3.0 mm, 3.5 mm, 4.0 mm, 4.5 mm, 5.0 mm, 5.5 mm, and 6.0 mm. Calibrated stones enable mass production of jewellery.

Calibrated sizing is especially important for channel-set and pavé-set jewellery, where dozens of identically sized stones must sit flush in pre-cut grooves. Lab-grown diamonds are frequently supplied calibrated, since controlled growth makes it easier to plan target sizes.

The standard unit of weight for gemstones and diamonds. One carat equals exactly 0.200 grams (200 milligrams). Each carat is subdivided into 100 points — so a 0.75 ct diamond is sometimes called a '75-pointer'. Carat weight directly influences price, especially as diamonds cross key thresholds such as 0.50, 0.75, 1.00, 1.50, and 2.00 carats.

The word 'carat' derives from the carob seed (Ceratonia siliqua), historically used as a counterweight on balance scales. The metric carat was standardised internationally in 1907. Note that carat (gemstone weight) is spelled differently from karat (gold purity) — a common source of confusion.

A grading criterion that assesses the presence, size, nature, position, and number of internal characteristics (inclusions) and external characteristics (blemishes) in a diamond. GIA's clarity scale runs from Flawless (FL) — no inclusions or blemishes visible under 10× magnification — through IF, VVS1, VVS2, VS1, VS2, SI1, SI2, to Included (I1, I2, I3).

Clarity is assessed by a trained grader under 10× magnification. The nature of an inclusion matters as much as its size. An eye-clean VS2 and an eye-clean SI1 may look identical to the naked eye, yet carry significantly different prices — understanding clarity grades helps buyers find value.

The tendency of a crystalline mineral to break along specific flat planes of atomic weakness, producing smooth, flat surfaces. Diamond has perfect octahedral cleavage in four directions, corresponding to the four octahedral faces of its crystal structure. While diamond is the hardest mineral, this cleavage makes it possible to cleave — and vulnerable to sharp blows in the cleavage direction.

Diamond cleavage was historically exploited in cutting: cleaving a rough diamond along its natural planes was the primary method of dividing large rough crystals before sawing technology improved. A sharp impact on a diamond's corner in the cleavage direction can cause it to split — which is why princess cut corners require protective prongs.

A standardised measure of the absence of colour in a white diamond. GIA's D-to-Z colour scale ranges from D (perfectly colourless) through near-colourless (E–J), faint (K–M), very light (N–R), to light yellow or brown (S–Z). The more colourless a diamond, the rarer and generally more valuable it is — provided other quality factors are equal.

Colour grading is performed face-down against a white grading trough under calibrated daylight-equivalent lighting, using master comparison stones. Lab-grown diamonds follow the same D-to-Z scale. Fancy-coloured diamonds are graded on a completely separate scale based on hue, tone, and saturation.

The angle between the bezel (kite) facets of a diamond's crown and the horizontal girdle plane. For round brilliants, the ideal crown angle range is approximately 31.5°–36.5°, with 34.5° often cited as the sweet spot for balancing brilliance and fire. Crown angle interacts critically with pavilion angle — together they determine a diamond's overall optical performance.

Crown angle is the primary determinant of fire (spectral colour flashes). A steeper crown angle and smaller table produce more fire; a shallower crown angle and larger table produce more brilliance. GIA's cut grade model evaluates many thousands of crown/pavilion combinations across a range — not a single fixed proportion.

A mineral crystal trapped inside a diamond during its formation. Crystal inclusions may consist of other diamonds (tiny diamond crystals trapped inside the host), garnets, diopside, olivine, or other minerals present in the mantle during growth. They appear as small, three-dimensional shapes under magnification and are plotted as red circles on GIA clarity diagrams.

The presence of specific mineral inclusions (such as majorite garnet) can confirm a diamond's natural mantle origin, distinguishing it from a lab-grown stone. Crystal inclusions generally affect clarity more than feathers of similar size because they are often higher-relief.

The small facet (or pointed tip) at the very bottom of a diamond's pavilion. In modern cutting, most round brilliants have no culet — the pavilion facets meet at a point. A culet facet was standard in older cuts (such as old European and old mine) to prevent chipping at the tip, but it appeared as a dark circle when viewed through the table. GIA reports grade culet from None to Very Large.

A large culet was a hallmark of antique cuts and is now considered undesirable in modern stones because it creates a visible 'open' circle in the centre. However, collectors of antique and estate jewellery specifically look for open culets as period-authentic features.

A square or rectangular brilliant-cut diamond with rounded corners and curved sides, giving the outline a 'cushion' or pillow shape. The cushion cut evolved from the old mine cut and typically features larger facets than a round brilliant, producing a distinct chunky sparkle pattern. It exists in two main variants: cushion brilliant and cushion modified brilliant (also called 'crushed ice').

Cushion cuts are the third most popular diamond shape. The 'crushed ice' variant has become particularly popular for lab-grown diamonds. Length-to-width ratio: 1.00–1.09 is square; 1.10–1.20 is slightly rectangular.

A GIA assessment of how well a diamond's facets interact with light. Cut grade applies to round brilliant diamonds and runs from Excellent — the top 3% of diamonds — through Very Good, Good, Fair, and Poor. It incorporates three sub-grades: Polish, Symmetry, and a calculated prediction of the diamond's brightness, fire, and scintillation based on its proportions.

Cut is widely regarded as the most important of the 4Cs for visual impact, since even a colourless, flawless diamond will appear dull if poorly cut. GIA introduced its cut grading system for round brilliants in 2005. Non-round shapes do not have an official GIA cut grade.

Chemical Vapor Deposition — one of the two primary methods used to grow lab diamonds. A thin diamond seed plate is placed inside a chamber filled with carbon-rich gas (typically methane). Microwave energy breaks the gas molecules apart, and carbon atoms deposit layer by layer onto the seed, crystallising into diamond. CVD typically operates at lower pressures than HPHT and allows precise control of crystal growth.

CVD-grown diamonds can sometimes exhibit brown or grey tinting from internal graining, which producers may correct with post-growth HPHT treatment. Modern CVD diamonds are essentially indistinguishable from natural diamonds without advanced spectroscopic equipment.

The total depth of a diamond (from table to culet, in millimetres) divided by the average girdle diameter, expressed as a percentage. For a round brilliant, the ideal depth percentage falls roughly between 59% and 62.5%. Stones that are too deep lose light through the sides; stones that are too shallow create a 'nail-head' dark centre.

Depth percentage is one of the key proportion data points listed on grading reports. Along with table percentage, crown angle, and pavilion angle, it forms the proportion fingerprint that graders and cut-evaluation tools use to predict optical performance.

A gemstone composed entirely of carbon atoms arranged in a cubic crystal lattice — the diamond cubic structure. Diamond is the hardest natural substance known (Mohs 10) and has the highest thermal conductivity of any natural material at room temperature. Its extraordinary refractive index (2.417) and high dispersion produce the optical properties prized in jewellery. Diamonds form deep within the Earth's mantle under extreme pressure (45–60 kbar) and temperature (900–1,300 °C).

The word 'diamond' comes from the ancient Greek adámas — 'unbreakable'. Despite their hardness, diamonds have perfect octahedral cleavage in four directions. Both natural and lab-grown diamonds are chemically and physically identical — differentiated only by their origin.

A detailed document produced by an independent gemological laboratory (GIA, IGI, HRD, GCAL, etc.) that records a diamond's 4Cs and other key characteristics including shape, measurements, depth and table percentages, girdle description, culet, polish, symmetry, fluorescence, clarity plot, and proportion diagram. A grading report is an objective, third-party assessment that facilitates trust in diamond transactions.

Grading reports are not valuations — they do not state a dollar value. They are scientific assessments of quality. The word 'certificate' is technically incorrect (laboratories certify graders, not stones), but it is universal in consumer usage. GIA and IGI both issue separate Natural and Laboratory-Grown report designs.

The optical property of a gem material to separate white light into its spectral components (rainbow colours) by refracting different wavelengths at slightly different angles. Diamond's dispersion is 0.044; moissanite's is 0.104. High dispersion produces the visual effect known as fire.

Dispersion and fire are closely related but technically distinct — dispersion is the measurable physical property of the material; fire is the visual effect produced by dispersion in a cut stone. Sphene, demantoid garnet, and zircon have higher dispersion than diamond.

A gemstone assembled from two separate layers bonded together, designed to imitate or enhance the appearance of a more valuable stone. A classic example is a garnet-topped doublet: a thin slice of natural garnet cemented onto coloured glass. Doublets can also pair two genuine gemstone layers — such as a natural opal slice mounted on a backing to increase durability.

Doublets must be disclosed at point of sale. Detection typically involves examining the stone at the girdle under magnification for the glue line or junction between layers. Doublets are legitimate when sold transparently, but constitute fraud if sold as natural single-origin stones.

A rectangular step-cut diamond with cropped corners, originally developed for cutting emeralds and later applied to diamonds. The emerald cut features long, parallel step facets arranged in tiers on both the crown and pavilion, producing a distinctive 'hall of mirrors' effect rather than the sparkle pattern of brilliant cuts.

The emerald cut's open, large facets make clarity highly visible: inclusions that would be hidden in a brilliant cut are easily seen. VS2 or better is typically recommended. The elongated shape creates a 'finger-lengthening' illusion. Length-to-width ratio is typically 1.30–1.50 for classic proportions.

An inclusion that is visible to the unaided human eye without magnification when the diamond is viewed face-up at normal viewing distance (~25–30 cm). A diamond with an eye inclusion is not considered eye-clean. Eye inclusions are typical of SI2 and Included (I1, I2, I3) clarity grades.

The visibility of an inclusion depends not just on its size but also on its nature (white/transparent vs black/opaque), position (central under the table vs near the girdle), and relief (contrast against surrounding diamond).

A descriptor for a diamond or gemstone in which no inclusions are visible to the unaided human eye when viewed face-up at a normal viewing distance of approximately 25–30 cm (10–12 inches). Eye-clean is not an official GIA grade but is widely used in trade to identify stones where inclusions do not affect visual appearance. Most VS1, VS2, and many SI1 diamonds are eye-clean.

At Azena Gems, all stones sold in jewellery settings are verified eye-clean under standard viewing conditions. Eye-clean SI1–SI2 diamonds offer excellent value since their inclusions are invisible during wear but command significantly lower prices than VS-grade equivalents.

A small internal fracture or break inside a diamond, often partially healed, that resembles a feather when viewed under magnification. Feathers are one of the most common types of diamond inclusion and can appear as transparent, white, or reflective planar breaks. They range from tiny surface-reaching fractures to larger internal planes that may affect durability.

A feather that reaches the surface is a durability concern — if struck along the cleavage direction, such a feather could propagate. GIA plots feathers as red lines on clarity diagrams. Feathers in the SI1–SI2 range are common, and whether they are acceptable depends on size, position, and orientation.

A type of inclusion consisting of a partially healed fracture inside a diamond that has been infilled with fluid or solid material during the diamond's geological history, leaving a pattern resembling a human fingerprint. Fingerprint inclusions are flat, disc-shaped features with radiating or concentric lines of tiny fluid or gas pockets visible under magnification.

Fingerprint inclusions are unique to natural diamonds — they form from the partial re-healing of fractures while the diamond was still deep in the mantle. Their presence can be used as one indicator of natural diamond origin.

The rainbow-coloured flashes of light emitted by a diamond when white light is separated into its spectral components as it passes through the stone. Fire is produced by a diamond's high dispersion value (0.044). A well-cut diamond with good crown angles and a smaller table shows more fire; a larger table or shallower crown suppresses it.

Fire is most visible under point-light sources (candlelight, spotlights) rather than diffuse overhead lighting. Moissanite has even higher dispersion (0.104) than diamond, producing more fire — this is actually one way gemologists distinguish the two.

A diamond's ability to emit visible light — most commonly blue — when exposed to ultraviolet (UV) radiation. Fluorescence is assessed by grading labs on a scale of None, Faint, Medium, Strong, and Very Strong. Approximately 25–35% of gem-quality diamonds exhibit some degree of fluorescence.

In lower-colour diamonds (I–M), strong blue fluorescence can make the stone appear whiter in natural light. In high-colour stones (D–F), strong fluorescence may cause a milky or hazy appearance, which commands a price discount. GIA research has shown fluorescence has no measurable effect on optical performance in the vast majority of cases.

An irregular break in a gemstone that does not follow the mineral's natural cleavage planes. In diamond, fractures produce conchoidal (shell-like), stepped, or granular surfaces rather than the flat mirror-like planes of cleavage breaks. A feather is a specific type of fracture inside a diamond.

The term 'fracture' is sometimes used interchangeably with 'feather' in the diamond trade, though technically they differ: cleavage produces flat, mirror-like planes; fracture produces irregular, rough surfaces. GIA does not grade fracture-filled diamonds.

Gem Certification & Assurance Lab — a New York-based diamond grading laboratory founded in 2001, known for its '100% Guarantee' on all grading assessments. GCAL reports include a full optical performance report with brightness, fire, scintillation, and light symmetry maps generated by proprietary imaging technology. GCAL was acquired by Sarine Technologies in 2022.

GCAL's optical report provides photographic and measurable proof of a diamond's light performance, going beyond the proportion-based assessments of GIA and IGI. GCAL is particularly used by US retailers. Their guarantee means that if a consumer's independent assessment differs, GCAL will compensate for the difference.

An educational and/or testing institution dedicated to the scientific study, grading, and research of gemstones. The term most commonly refers to the Gemological Institute of America (GIA), though many countries have their own institutes — including the Gemmological Association of Great Britain (Gem-A, which offers the FGA designation) and others.

Professional gemological credentials include GIA's Graduate Gemologist (GG), Gem-A's FGA, and IGI's Graduate Gemologist programmes. In the trade, 'GIA-trained' is widely used as shorthand for rigorous gemological education.

A mineral, rock, or organic material that is cut, polished, and used in jewellery or ornamentation, prized for its beauty, rarity, or durability. Diamonds, rubies, emeralds, and sapphires are traditionally called 'precious stones'; all others are called 'semi-precious' — though this distinction is not scientifically meaningful and is falling out of use.

The gem world encompasses thousands of mineral species, but only about 130 are used in jewellery with any regularity. Hardness, durability, clarity, colour, and availability all determine commercial significance.

The Gemological Institute of America — the world's most respected nonprofit gem grading laboratory and educational organisation, founded in 1931. GIA developed the modern 4Cs grading system, the International Diamond Grading System™, and is recognised as the global authority on diamond and coloured gemstone research. GIA grading reports are the most widely trusted and accepted in international diamond trading.

GIA operates grading laboratories in New York, Carlsbad, Antwerp, Mumbai, Hong Kong, Bangkok, Ramat Gan, and other global locations. GIA does not sell diamonds — it only grades and certifies them.

The narrow band or edge around the widest part of a faceted diamond, separating the crown (top) from the pavilion (bottom). The girdle is the portion that sits inside a jewellery setting's prongs or bezel. Girdle thickness is described on GIA reports on a scale from Extremely Thin to Extremely Thick. An ideal girdle is Thin to Slightly Thick; a very thin girdle is vulnerable to chipping.

The girdle can be faceted (a series of small flat facets), bruted (rough, granular texture), or polished (smooth and glass-like). A faceted girdle is considered the premium option. The girdle diameter is the reference dimension for setting-size matching.

A fancy-shaped brilliant-cut diamond in the form of a heart, with a cleft at the top (created by two rounded lobes) and a single point at the bottom. The heart shape is one of the most technically demanding fancy cuts — the two lobes must be perfectly symmetrical, the cleft sharp and even, and the tip clean. Heart cuts typically have 59 facets and are most effective at 0.50 ct or larger.

Below 0.30 ct, the heart outline becomes difficult to distinguish to the naked eye. The heart cut is primarily associated with romantic jewellery (pendants, solitaire rings). Length-to-width ratio of 0.90–1.10 is considered ideal.

High Pressure High Temperature — a process used both to grow lab diamonds and to treat natural diamonds. In synthesis, a diamond seed is placed in a growth cell with a carbon source and metal catalyst under pressures of 50–65 kbar and temperatures of 1,300–1,600 °C, mimicking the conditions under which natural diamonds form in the Earth's mantle. As a treatment, HPHT can improve the colour of certain brownish diamonds.

HPHT was the first commercially viable method for growing synthetic diamonds, pioneered by GE in 1954. HPHT-grown diamonds tend to have a cubic or cuboctahedral crystal habit, with metallic inclusions (iron, nickel, cobalt) from the catalyst — detectable under a strong magnet and via spectroscopy.

HRD Antwerp (formerly Hoge Raad voor Diamant — Diamond High Council) is a Belgian diamond grading laboratory headquartered in Antwerp, the historic global centre of the diamond trade. HRD provides diamond grading reports, certificates, and educational programmes. Its reports are widely accepted in the European and Middle Eastern diamond markets.

HRD was founded in 1973 by the Belgian diamond industry. Its grading standards align closely with GIA in terms of 4Cs assessment. Antwerp handles approximately 80% of the world's rough diamond trade by volume, making HRD a strategically important certification body.

A round brilliant diamond cut to the specific proportions mathematically derived by Marcel Tolkowsky in 1919 for optimal balance of brilliance and fire. The original Tolkowsky ideal specifies: table ~53%, crown angle 34.5°, pavilion angle 40.75°, total depth ~59.3%. Modern interpretations have been refined through GIA's extensive research and computer modelling.

The term 'ideal cut' is used both to describe Tolkowsky's original 1919 specifications and, more broadly, any round brilliant in the top performance tier. The American Gem Society Laboratories (AGSL, now part of GIA) formally grades round brilliants as AGS Ideal (0) — their top grade.

The International Gemological Institute — one of the world's largest gem grading laboratories, founded in Antwerp in 1975. IGI operates laboratories in Antwerp, New York, Mumbai, Los Angeles, Dubai, Tokyo, Bangkok, Hong Kong, Tel Aviv, and other major centres. IGI grades both natural and lab-grown diamonds and is one of the most commonly used labs for certifying lab-grown diamond jewellery.

IGI is the dominant certification lab for lab-grown diamonds at the retail level, particularly in the US, India, and Europe. IGI was acquired by the De Beers Group-related entity Lab Grown Group in 2023.

Any internal characteristic within a diamond or gemstone formed during its growth. Inclusions originate during crystallisation and include crystal inclusions (trapped mineral crystals), feathers (fractures), clouds (clusters of minute pinpoints), needles, graining, cavities, and laser drill holes. The size, type, location, and number of inclusions determine a stone's clarity grade.

The term 'inclusion' replaces the older word 'flaw' — because inclusions are natural growth features, not defects, and their presence records the geological history of the stone. In diamonds, inclusions near the girdle or pavilion are less visible in finished jewellery than central table inclusions.

Two commonly confused terms with distinct meanings. Carat (ct) is a unit of weight for gemstones — 1 carat = 0.200 grams. Karat (K or kt) is a unit of gold purity — 24 karats represents pure gold (99.9%+), 18K is 75% gold, 14K is 58.3% gold, and 9K is 37.5% gold. In British English, 'carat' was historically used for both, which adds to the confusion.

A common practical pairing: an 18-karat gold ring set with a 1-carat diamond. The ring's gold purity is 75%; the diamond weighs 0.2 grams. In German-speaking markets, both are written 'Karat', so context determines meaning.

A diamond grown in a controlled laboratory environment using either CVD or HPHT technology. Lab-grown diamonds are chemically, physically, and optically identical to natural diamonds — both are pure carbon in a diamond cubic crystal structure. They are graded by the same 4Cs standards and certified by the same laboratories (GIA, IGI, HRD, GCAL). The sole difference from natural diamonds is their origin.

The FTC ruled in 2018 that lab-grown diamonds are real diamonds. Lab-grown diamonds typically sell at a 60–80% discount to equivalent natural diamonds. At Azena Gems, lab-grown diamonds carry full IGI certification and are clearly disclosed as laboratory origin.

Abbreviation for Lab-Grown Diamond, widely used in the trade, on grading reports, and in product listings. Interchangeable with 'laboratory-grown diamond', 'lab diamond', or 'cultured diamond'. Grading reports from GIA and IGI will state the growth origin explicitly (e.g., 'Laboratory-Grown') rather than 'LGD', but the abbreviation is standard shorthand in B2B and retail communications.

When referencing a specific stone, the format is typically: 1.00 ct LGD, Round Brilliant, D/VVS1, Ex/Ex/Ex, IGI.

A trade term for a diamond or gemstone that is entirely free of visible inclusions or blemishes when examined under 10× magnification with a standard jeweller's loupe. A loupe-clean stone is equivalent to a GIA VVS or higher clarity grade in practical terms. Not an official laboratory grade.

'Loupe-clean' is a stricter standard than 'eye-clean' — it means the stone would satisfy even an expert who checks it carefully under magnification. In coloured stone trading, 'loupe-clean' is a common positive descriptor and can command a premium.

A boat-shaped fancy brilliant-cut diamond with two pointed ends and a curved outline. The marquise cut was reportedly commissioned by King Louis XV of France in the 18th century. It has 55 facets and is notable for maximising perceived size — the elongated shape creates an illusion of greater carat weight per millimetre of face-up surface than a round brilliant of equal weight.

The marquise cut is vulnerable to the 'bowtie effect' — a dark bowtie-shaped shadow across the stone's width visible in face-up view. Ideal length-to-width ratio is 1.75–2.25. Pointed ends require protective V-prongs.

Small diamonds, typically under 0.20 carats (20 points) and sometimes defined more narrowly as under 0.18 ct, used as accent or side stones in jewellery settings. Melee is typically sold by total carat weight in parcels rather than individually, sorted by size using sieves. A diamond halo ring may contain 30–50 melee stones contributing significantly to the ring's total carat weight.

Melee is traded in matched parcels — stones sorted by sieve size (e.g., +5/−5.5 sieve), colour, and clarity. In the lab-grown diamond sector, melee pricing has dropped sharply since 2020 due to rapid production scale-up. Azena Gems supplies matched natural and lab-grown melee parcels to B2B jewellery manufacturers in Hungary, Poland, and Slovakia.

A diamond cut that combines brilliant-cut facets on one part of the stone with step-cut facets on another. The most common configuration is a brilliant-cut crown with a step-cut pavilion — or vice versa — seeking to combine the fire and sparkle of a brilliant with the clarity window and elegance of a step cut.

The oval brilliant, radiant cut, and princess cut are all technically modified brilliants, not pure mixed cuts. True mixed cuts combining step crown and brilliant pavilion are less common in modern production but historically were used to retain rough weight while accommodating unusual crystal shapes.

A relative scale from 1 to 10 measuring a mineral's resistance to scratching, developed by German mineralogist Friedrich Mohs in 1812. The scale is based on ten reference minerals: 1 (Talc) → 2 (Gypsum) → 3 (Calcite) → 4 (Fluorite) → 5 (Apatite) → 6 (Orthoclase) → 7 (Quartz) → 8 (Topaz) → 9 (Corundum/Sapphire/Ruby) → 10 (Diamond).

The Mohs scale is ordinal, not linear — diamond (10) is approximately 4× harder than sapphire (9) in absolute scratch resistance. Hardness above 7 (quartz dust) is recommended for everyday jewellery wear. Diamond's Mohs 10 makes it ideal for daily-wear pieces.

A naturally occurring silicon carbide mineral (SiC) and its laboratory-grown counterpart, widely used as a diamond alternative. Natural moissanite was first discovered in 1893 by Henri Moissan in a meteorite crater in Arizona. Moissanite has a Mohs hardness of 9.25–9.5, a refractive index of 2.65–2.69 (higher than diamond), and dispersion of 0.104 (more than double diamond's 0.044).

Because natural moissanite is exceedingly rare, all commercial moissanite is lab-grown. It passes some diamond testers (thermal testers) but fails multi-wave testers. Moissanite is sold openly as a diamond alternative at a fraction of the price and is a legitimate gemstone choice in its own right.

A diamond formed through geological processes deep within the Earth's mantle over billions of years — typically 1–3.5 billion years ago — and transported to the surface by volcanic kimberlite or lamproite eruptions. Natural diamonds are distinguished from lab-grown diamonds solely by origin; both share identical chemical composition, crystal structure, hardness, and optical properties.

Natural diamonds form under pressures of approximately 45–60 kbar and temperatures of 900–1,300 °C at depths of 150–250 km. They carry Type classifications (Ia, IIa, IIb, IaB) based on nitrogen and boron content, which gemologists use alongside spectroscopy to confirm natural origin.

A long, thin, rod-shaped crystal inclusion inside a diamond, resembling a needle when viewed under magnification. Needles are typically white or transparent and consist of a single crystal (often a small mineral or a diamond crystal elongated along a growth axis). Individual needles are minor clarity features; clusters of needles are sometimes called 'graining' or 'growth tubes'.

Needles most commonly affect VS and SI clarity grades. A single needle in a 1.00 ct SI1 is typically invisible to the naked eye. Needles plotted on GIA reports appear as fine red lines oriented along the crystal's growth direction.

A historical diamond cut popular from the 17th to early 20th centuries, characterised by a high crown, small table, large open culet, cushion-shaped girdle outline, and a deep pavilion. Old mine cuts were shaped by hand to match the natural octahedral crystal form of rough diamonds, cut by eye rather than by precise mechanical measurements. The result is an organic, asymmetric beauty prized in antique and estate jewellery.

Old mine cuts are the direct ancestor of the modern cushion cut. Under candlelight, old mine cuts produce a romantic, warmer glow compared to the bright, high-contrast sparkle of modern brilliants. They are highly collectible and often recut into modern shapes.

An elliptical brilliant-cut diamond that delivers the brilliance and fire of a round brilliant in an elongated shape. The oval cut was developed by Lazare Kaplan in 1957 and typically has 57–58 facets. Ovals create an elongating visual effect when set in rings, and their larger face-up surface area makes them appear approximately 10% larger than a round brilliant of equal carat weight.

Like marquise and pear cuts, ovals are susceptible to the 'bowtie effect' — a dark shadow across the stone's width. The severity of the bowtie varies with cutting proportions and is not listed on grading reports. Ovals have no GIA cut grade; in-person or video inspection is essential.

The lower section of a faceted gemstone below the girdle, terminating at the culet. In a round brilliant, the pavilion comprises the eight pavilion main facets, sixteen lower-girdle facets, and the culet. The pavilion angle — the angle between the pavilion mains and the girdle plane — is the single most important proportion for light return; ideal range for a round brilliant is approximately 40.6°–41.0°.

The pavilion acts as the main reflective engine of the diamond. Light entering through the crown hits the pavilion facets, ideally undergoing total internal reflection and bouncing back up through the crown. If the pavilion is too deep, light leaks through the sides; too shallow, and a dark 'nail-head' pattern appears.

A teardrop-shaped fancy brilliant-cut diamond combining the rounded body of an oval with a single pointed tip. The pear cut has 57–58 facets and is most commonly used in pendants and earrings, where the point faces downward for an elegant drop effect. In rings, it is typically set with the point toward the fingertip, creating an elongating illusion.

The pear's asymmetric shape requires attention to shoulder balance and lobe symmetry. Like other elongated shapes, the pear is susceptible to the bowtie effect. Ideal length-to-width ratio is 1.45–1.75 for a classic teardrop shape. The pointed tip requires a protective V-prong.

A GIA sub-grade assessing the smoothness and quality of a diamond's facet surfaces after cutting. Polish is graded Excellent, Very Good, Good, Fair, or Poor. Excellent polish means facets are mirror-smooth with no visible surface irregularities under 10× magnification. Poor polish features scratches, burns, rough girdle, or abrasion visible even to the naked eye.

Polish is one of the three components of GIA's overall cut grade for round brilliants (alongside Symmetry and the proportions-based assessment). A diamond graded Ex/Ex — 'triple excellent' — represents the top tier of craftsmanship.

A square or rectangular brilliant-cut diamond with sharp, uncut corners and a modified brilliant-cut facet arrangement. The princess cut was developed in the 1960s–1970s and became the second most popular diamond shape after round brilliant. It retains more of the rough diamond's original crystal octahedron than a round — typically yielding 60–80% rough weight — making it more cost-efficient per carat. The four sharp, unprotected corners are its primary vulnerability; princess cuts should be set in four-claw prong settings with individual corner prongs.

Princess cuts are graded by GIA with standard 4Cs assessments but without an official cut grade (only round brilliants receive one). A well-fitted setting slightly overlaps each corner with a claw tip, protecting the exposed crystal structure. Buyers should inspect princess cut girdle edges under magnification when purchasing pre-owned rings, as corner chips are common.

A rectangular or square brilliant-cut diamond with cropped corners and a brilliant-cut facet pattern on both crown and pavilion, developed by Henry Grossbard in 1977. The radiant cut combines the rectangular outline of an emerald cut with the brilliant facets of a round or princess cut, producing high brilliance, fire, and scintillation in a step-like outline. It has 70 facets and was the first rectangular cut specifically designed for maximum light performance.

The radiant cut is an excellent choice for buyers who want the elongated emerald cut aesthetic with the sparkle of a brilliant. Its facet pattern breaks up light more aggressively than a step cut, making it more forgiving of lower clarity grades. Ideal length-to-width ratio is 1.00–1.05 for square; 1.25–1.50 for rectangular.

The Rapaport Diamond Report — the diamond industry's most widely used wholesale price benchmark, published weekly by Rapaport Group since 1978. The 'Rap sheet' lists per-carat prices for round and pear-shaped natural diamonds across various weight ranges, colour grades, and clarity grades. Actual transaction prices are typically quoted as a percentage discount relative to Rapaport: e.g., '−20% Rap' means 20% below list price.

Rapaport is not an exchange — it does not execute trades. It is a price reference that establishes a common benchmark across the global trade. For lab-grown diamonds, Rapaport does not maintain an equivalent published list; pricing is driven by platform-specific supply-demand.

A numerical measure of how much a gemstone bends (refracts) light as it passes from air into the stone. Diamond has a refractive index of 2.417 — exceptionally high — meaning light bends sharply when entering and exiting the crystal, contributing to diamond's characteristic brilliance. The RI is a fundamental physical constant used by gemologists to identify unknown gemstones.

RI is measured with a refractometer. Most transparent gemstones have RIs between 1.4 and 2.0; diamond's 2.417 is among the highest of all natural gems. The high RI is directly responsible for total internal reflection — the phenomenon where light hitting the pavilion at below the critical angle (~24.4° for diamond) is reflected back upward rather than escaping.

A diamond in its natural, uncut, and unpolished crystalline state as extracted from the kimberlite pipe or alluvial deposit — or as grown from a CVD or HPHT process. Rough diamonds typically have octahedral, dodecahedral, or cubic crystal forms. They are assessed for sawability, cleave direction, inclusions, shape, and potential yield before cutting decisions are made.

The journey from rough to polished involves planning (using 3D scanning software like Sarin or Helium), cleaving or sawing, bruting, and faceting. Rough diamond prices are driven by crystal quality, size, colour, and shape.

The most popular and scientifically optimised diamond cut, featuring 57 or 58 facets (58 if a culet facet is present) arranged symmetrically around the stone's circular girdle. The round brilliant was mathematically defined by Marcel Tolkowsky in 1919 and has since been refined through GIA research into the ideal proportions for maximum brilliance, fire, and scintillation.

Round brilliants account for approximately 70–75% of all diamond sales worldwide. They receive GIA's full cut grade assessment. Rounds have lower rough-yield than fancy shapes — typically 35–45% — which partly explains their premium.

A brand of automated diamond measurement and planning technology produced by Sarin Technologies Ltd (Israel). Sarin machines use laser profilometry to create a three-dimensional digital model of a diamond or rough crystal, producing precise proportion data (table %, depth %, crown angle, pavilion angle, girdle thickness, culet) and a light performance analysis. Sarin is the industry-standard tool for rough planning and polished proportion verification.

Sarin reports are widely used by cutters, traders, and laboratories to verify proportions that feed into cut grade calculations. For rough diamonds, Sarin planning software identifies the optimal cut to maximise value. Sarin Technologies also owns GCAL (since 2022).

The flashes of light — and contrast between bright and dark areas — observed when a diamond, the observer, or a light source moves. Scintillation has two components: flash scintillation (the sparkle of white and coloured light flashes) and pattern scintillation (the static arrangement of light and dark areas visible in the diamond's face-up appearance). Both are directly influenced by facet arrangement and cut precision.

In practical terms, scintillation is what makes a diamond appear to 'dance' under changing light conditions. Larger facets produce fewer but more dramatic flashes; smaller facets produce more numerous but subtler flashes.

A surface-reaching graining feature that appears as a faint line on a polished diamond facet, caused by irregular crystal growth directions meeting at a boundary. Seams are a type of grain-related blemish visible only under specific lighting and magnification conditions. They differ from scratches in that they are structural features within the crystal lattice.

Seams and grain lines are most commonly seen in Type IIa diamonds, which are often colourless and high-purity but can have more complex growth histories. If a seam extends below the surface, it may be classified as an internal graining inclusion rather than a surface blemish.

Slightly Included — two GIA clarity grades (SI1 and SI2) indicating that inclusions are noticeable under 10× magnification but may or may not be visible to the unaided eye. SI1 inclusions are typically small, few, and positioned away from the centre; many SI1 diamonds are eye-clean. SI2 inclusions are larger or more numerous; some are visible to the naked eye, particularly in stones over 1.00 ct.

SI clarity is the most popular clarity range for diamond buyers seeking value — particularly SI1 — because eye-clean specimens can be found significantly below the VS grade premiums. At Azena Gems, SI1–SI2 lab-grown diamonds are individually verified for eye-cleanliness before being offered in finished jewellery.

A precision mesh screen used to sort small diamonds and gemstones by size. Diamond sieves consist of a series of metal or nylon screens with circular holes of standardised diameters. A stone is placed on a sieve: if it falls through the holes, it is smaller than that sieve; if it is retained, it is larger. Standard sieve sizes correspond to ranges in stone diameter and approximate carat weight.

Sieve sorting is essential in melee trading because buyers and sellers need to specify stone size consistently. A '+4/−4.5 sieve round brilliant' means the stone's diameter is between 4.0 mm and 4.5 mm, corresponding approximately to 0.23–0.34 ct. Lab-grown melee parcels at Azena Gems are sieve-sorted and colour/clarity matched before supply.

An inclusion within a diamond that consists of a mineral softer than diamond itself — meaning that if the diamond's surface were to be polished over the inclusion site, the soft mineral would be removed preferentially, leaving a pit or cavity. Common soft inclusions include graphite (carbon in a non-diamond structure), calcite, and some silicate minerals.

Graphite inclusions in diamonds are of particular interest — they represent carbon that crystallised in a non-diamond structure. They appear as black, opaque pinpoints or irregular masses. If a graphite inclusion reaches the surface, polishing may create a surface pit classified as a cavity or blemish.

A general consumer term describing the overall visual liveliness and light performance of a diamond, encompassing brilliance (white light return), fire (spectral colour flashes), and scintillation (movement flashes and contrast patterns). Sparkle is not a technical grading term but is widely used in retail to communicate the combined optical effect of all three light properties working together.

In trade and gemological contexts, 'sparkle' is sometimes used more specifically to mean scintillation alone. Cut quality, stone size, surface cleanliness, and lighting environment all influence perceived sparkle.

A faceting style in which the facets are arranged in parallel, trapezoidal rows or 'steps' on both the crown and pavilion, all parallel to the girdle. Unlike brilliant cuts whose facets radiate outward from the centre, step cuts produce long, flat reflections that create a 'hall of mirrors' or 'art deco' visual character. The emerald cut and asscher cut are the most prominent step cuts in the diamond trade.

Step cuts are less forgiving of clarity issues than brilliant cuts, because their large, flat facets act as windows that expose the stone's interior clearly. They are also more revealing of colour. VS2 or higher clarity and F–H or better colour is ideal.

Internal graining lines just below the surface of a polished diamond facet, caused by irregular or accelerated crystal growth producing variations in atomic density along specific directions. Sub-surface graining appears as faint parallel lines or a hazy, layered appearance just beneath the facet surface, visible under magnification at specific lighting angles.

Sub-surface graining is most commonly encountered in Type IIa diamonds and in certain HPHT-treated and HPHT-grown diamonds. It is noted on GIA reports as an internal clarity characteristic. Significant sub-surface graining may limit how cleanly certain facets can be polished — affecting polish grade.

A GIA sub-grade assessing the precision and exactness of a diamond's shape and the arrangement, alignment, and size uniformity of its facets. Symmetry is graded Excellent, Very Good, Good, Fair, or Poor. Excellent symmetry means facets meet perfectly at their junctions, the outline is geometrically consistent, and there are no deviations such as off-centre tables, wavy girdles, or extra facets.

Symmetry deviations affect both the visual appearance and the light patterns (specifically the eight-fold symmetry of the scintillation pattern in a round brilliant). Along with polish, symmetry forms part of GIA's 'make' assessment for cut grade.

The largest flat facet on the top (crown) of a diamond, positioned horizontally and parallel to the girdle. The table is the primary entry and exit point for light. Table percentage is the width of the table expressed as a percentage of the average girdle diameter — for a round brilliant, ideal range is approximately 54%–60%. A larger table allows more light in but can suppress fire by reducing the crown height.

The table facet is the only horizontal facet on a standard round brilliant — all other facets are angled. Table size interacts critically with crown angle: a slightly smaller table (54–57%) paired with a steeper crown angle (34–35°) produces excellent fire; a larger table (60–62%) with a shallower crown produces more brilliance but less fire.

Marcel Tolkowsky (1899–1991) was a Belgian-born mathematician and diamond cutter who, in 1919, published 'Diamond Design: A Study of the Reflection and Refraction of Light in a Diamond' — establishing the first mathematically derived ideal proportions for a round brilliant cut diamond. His calculations specified: table 53%, crown angle 34.5°, pavilion depth 43.1%, pavilion angle 40.75°, and total depth approximately 59.3%.

Tolkowsky came from a family of Antwerp diamond cutters and studied mathematics at Imperial College London. His thesis was a complete optical analysis of the round brilliant. While GIA's modern research has refined and broadened the 'ideal' range, Tolkowsky's proportions remain the philosophical foundation of excellent diamond cut quality.

A triangular growth or dissolution feature found on the natural crystal faces of rough diamonds, particularly on the octahedral faces. Trigons are shallow triangular indentations or ridges aligned with the diamond's crystal symmetry. Their presence confirms natural diamond crystallisation in the mantle.

Trigons are a key diagnostic feature used by gemologists to confirm natural diamond rough origin and distinguish it from synthetic rough. CVD and HPHT-grown rough crystals do not develop natural octahedral trigons.

Very Very Slightly Included — two GIA clarity grades (VVS1 and VVS2) indicating that inclusions are extremely difficult to detect even under 10× magnification, requiring significant effort even for an experienced grader. VVS1 inclusions are typically visible only from the pavilion view; VVS2 inclusions may be found in the crown view. Both grades are unquestionably eye-clean.

VVS diamonds represent a quality tier where the difference from IF is invisible except to a trained eye under 10× magnification — and completely invisible in real-world jewellery. In lab-grown diamonds, VVS grades are more readily available at accessible prices than in naturals, making VVS a practical choice for buyers seeking the cleanest possible stone.

The percentage of a rough diamond's original weight that is retained in the finished, polished stone. Yield is a primary economic driver in diamond cutting — higher yield from a given piece of rough means lower per-carat cost. Round brilliant cuts have the lowest typical yield (35–45%), while princess cuts and asscher cuts can achieve 60–80% yield.

Yield calculations must also account for polishing losses during grinding, sawing, and bruting. A rough diamond of 2.00 ct might yield a 0.85 ct round brilliant, or a 1.20 ct princess cut — a significant difference in material efficiency. In lab-grown diamond production, yield still matters: a CVD 'plate' that produces one 2.00 ct polished stone per growth cycle is more efficient than one yielding 1.50 ct.