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Our comprehensive Diamond Dictionary: Everything about diamonds

Here is everything you need to know on the subject of diamonds. Explore RenéSim's Diamond Dictionary and discover detailed information on the fascinating world of diamonds, with interesting facts on key topics including the Four Cs, diamond prices, the Kimberley Process and many other aspects of one of the most sought-after materials in the world.

You can find more interesting facts on the subject of jewellery in general in our Jewellery Lexicon. Consult our Gemstone Lexicon for in-depth information on precious stones.

The Four Cs

Find out everything about the Four Cs: Carat, Clarity, Colour & Cut.

Diamond Prices

Find out everything about diamond prices.


Diamond Dictionary

The Diamond 







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The word 'diamond' (from the Greek adamas, meaning 'invincible'), is known as the 'king of gems' because of its characteristic brilliance, its ability to reflect light (refraction and dispersion), its exceptional hardness and its rarity.


Diamond is a mineral composed of pure carbon, and
  • is the hardest known mineral, rating 10 on the Mohs scale of hardness. Its grinding hardness is 140 times greater than that of corundum (ruby, sapphire), which is rated 9 on the Mohs scale. However, the hardness of a diamond varies from face to face, so that a diamond can be ground using another diamond as the diamond powder used in this process contains every grade of hardness.

  • has the highest refraction index (2.42) of any optical material, and is the only optical material which reflects up to 100 per cent of incident light back in the same direction as the light source by means of double total reflection on the back wall of the brilliant. No other gemstone reflects such a great amount of light or sparkles so brilliantly.
  • is the best conductor of heat (even better than copper, for example!)

  • is an ideal investment. An ideal investment in this sense is one which retains all the advantages of a financial investment while eliminating its risks.


Diamonds form in the depths of the earth's mantel under very high pressure and at high temperatures, typically at a depth of around 150 to 300 kilometres and temperatures of 1,200 to 1,400 degrees Celsius. In volcanic eruptions, gas-rich rocks known as kimberlite or lamproite transport diamond-bearing fragments of the mantel to the surface and deposit them in channels known as volcanic pipes which are created in the eruptions. The diamonds are later mined from these pipes. Diamonds are thus xenocrysts, or 'foreign crystals', in kimberlite and lamproite deposits.


Only around one-quarter of all diamonds mined globally are of sufficient quality to be suitable as gemstones. Diamonds are therefore also widely used in a range of industrial processes, commonly as cutting edges for drills, cutting and grinding tools for industrial use, owing to their enormous hardness, abrasion-resistance and heat conductivity.


Diamonds are mined in two ways: they are washed out of accumulations of minerals, generally alluvial, known as 'placer deposits', or mined in the pipes of extinct volcanoes. In the latter process, the kimberlite-filled pipes are first excavated in open-cast mines and then excavated further from below in underground mines. The bedrock is crushed to release the diamonds.

Placer deposits' are boulder and sand sediments containing a recoverable concentration of detrital material. Detrital material is a geological term used to describe particles of rock or mineral grains formed from older rocks by processes of weathering and erosion. These particles are often transported into riverbeds, lakes or the ocean by sedimentation, forming sedimentary successions. A characteristic feature of detrital material including diamond is its resistance to weathering and its resilience. The diamonds are washed out of the placer deposits by special ships or dredged from the sea bed.
The concentration of diamond within the bedrock varies from deposit to deposit. The concentration in placer deposits is usually higher than in kimberlite pipes.


A diamond may well increase in value over time, depending on its size, colour and clarity. Finde out more about investment diamonds.

Go to Investors' Corner







Brilliants are diamonds cut in a special symmetrically round form with a minimum of 57 facets. The term (from the French for 'radiant' or 'lustrous') is often confused with 'diamond'; however, 'diamond' is applied to the raw gemstone (rough diamond) prior to receiving the brilliant cut. Developed in the early 20th century, this cut is designed to enhance the diamond with breathtaking lustre and beauty.

Go to Loose Brilliants



To find out about the unit of weight for diamonds, see Carat.



Diamonds require regular care. Even a light touch may deposit a film of grease that impairs their brilliance and radiance and rapidly attracts dust and dirt. In addition to having your diamonds professionally cleaned by a jeweller, we recommend using jewellery cleaner in liquid or tablet form or a mild washing-up liquid (dish soap) with a soft toothbrush. Rinse under running water and pat dry with a soft cloth.



A diamond certificate is always issued by a gemological institute and guarantees the authenticity of a diamond. It also contains a full description of the diamond's individual characteristics which determine its value. Certificates are always issued in English. The most highly respected laboratories / certification bodies include:

  • Gemological Institute of America(GIA)
    The world's largest certification authority for diamonds. The quality of its certificates is very high and is universally acknowledged throughout the industry.
  • Hoge Raad voor Diamant (HRD)
    This Belgian laboratory is the largest European certification authority for diamonds. The quality of its certificates is roughly equivalent to that of the GIA.
  • International Institute of Gemology (IGI)
    Headquartered in Antwerp, this Belgian institute operates 16 offices worldwide and is accordingly among the largest and most highly acknowledged certification authorities for diamonds.
  • European Gemological Laboratory (EGL)
    The globally operating Israeli laboratory is also among the acknowledged certification authorities worldwide.


Interpretation of the various certificates

The interpretation of internationally valid diamond assessment criteria can vary from one gemological institute to another. While institutes such as GIA, IGI and HRD are known for their rigorous interpretation, in some cases diamonds certified by EGL are assessed as 1 to 3 grades higher with respect to clarity or colour than they would be by other institutes. Although this by no means shows that EGL certified diamonds are poor or not recommendable, please note that for this reason EGL-certified diamonds are cheaper in most cases. For a fair price comparison you should therefore compare EGL-certified stones with GIA, IGI or HRD-certified stones of the same size that are assessed at 1 to 3 clarity or colour grades below the grade certified by EGL.



(Confédération Internationale de la Bijouterie, Joaillerie, Orfèvrerie, Perles et Pierres)
Association which defines globally approved commercial practices and valid rules for the jewellery industry.



For detailed information about the clarity of a diamond, see Clarity.



To find out about diamond colour, see Colour.



Describes the origin of a diamond which is mined under the provisions of the international Kimberley Process and is not used to finance arms or conflicts.



(See Kimberley Process)

The diamonds we supply are sourced exclusively from suppliers in member countries of the Kimberley Process and we strictly refuse any diamonds from illicit sources. RenéSim supplies only certified diamonds, enabling you to purchase with the confidence that your diamonds have not been used to fund conflicts.



The upper part of a diamond or gemstone (above the girdle).



The culet is the smallest facet at the bottom of a diamond. Ideally a diamond should come to a perfect point instead of having a culet. A culet that is too large or broken may be visible as a black dot when the diamond is viewed from above, impairing the beauty of the stone.

Drawing of diamond with culet, girdle and table



Detailed information on diamond cuts, cut grades and cut shapes.



Small, smooth and flat-cut faces of a diamond.



Used almost exclusively for transparent precious stones and gems. The faceted cut combines a large number of small facets (or flat faces). The majority are derived from one of two basic types: the round brilliant cut and the rectangular step cut.



  • Star of Africa or Cullinan I
    The largest cut diamond in the world, it is kept in the Treasury of the Tower of London.

  • Tiffany
    Found in 1878 in the De Beers Mine, the Tiffany Diamond was purchased by the famous jeweller of the same name. It is still in the possession of the family.

  • Blue Wittelsbach
    Believed lost in 1931, the Blue Wittelsbach Diamond was rediscovered in Antwerp in 1961 after an eventful history. It is owned by a wealthy collector.

  • Dresden Green
    Kept in the "Green Vault" of the National Art Collection of Dresden, the Green Dresden diamond is believed to originate from Brazil. Other opinions claim that the diamond is the 'green tear' of Shah Jahan (the builder of the Taj Mahal in Agra).

  • Hope Diamond
    The Hope Diamond is one of the most legendary and renowned diamonds in the world. The blue stone weighs 44.4 carats. It is said that the diamond was once in possession of the Indian god Vishnu, but was stolen from him; since that time the diamond has been under a curse bringing bad luck to all its owners. It was worn by the French monarchs Louis XIV and Louis XVI and Marie Antoinette, all of whom died under tragic circumstances. The stone was stolen again during the French Revolution and did not reappear until 1830, when it was purchased by Henry Philip Hope. Later owners of the Hope Diamond included Pierre Cartier and Harry Winston; the latter presented the stone to the Smithsonian Institute in Washington D.C. in 1958. The Hope Diamond is said to be worth between 200 and 250 million US dollars.



This term is used for diamonds with colours outside the classic grading scale for diamonds (e.g. green, blue, red, pink, canary yellow, brown). The colours are formed by impurities such as boron, nitrogen, hydrogen or radioactive radiation (green).



Fluorescence is the emission of light from a low-level light source when exposed to a higher-energy light source (e.g. ultra-violet light or even daylight in some cases). Diamonds with low to high fluorescence have a slight blue glow under ultra-violet light. Fluorescent diamonds (colourless or yellow) only emit light under ultra-violet rays and cease to do so when the ultra-violet source is removed. Diamonds have varying levels of fluorescence, from none at all to extremely strong. Highly fluorescent diamonds may have an oily or milky appearance in sunlight. A piece of jewellery set with several diamonds with differing levels of fluorescence may show irregular fluorescence under ultra-violet light.

A diamond with strong fluorescence is generally of lesser value but may have its own individual charm. In the case of coloured diamonds this can have a positive effect in comparison with colourless diamonds, and may significantly increase the attractiveness and value of the stones.



Consult this section for information on the four central criteria used in grading diamonds, the Four Cs: Cut, Carat, Colour und Clarity.



The girdle of a diamond is the circumference between the upper and lower part of the cut diamond, and thus its widest part. It determines the circumference and diameter of the diamond. We advise against diamonds with a Very Thin (or even Extremely Thin) girdle, which are vulnerable to chipping. A Very Thick or Extremely Thick girdle should also be avoided as it concentrates too much weight around the middle of the diamond and may make the stone appear smaller. The girdle should ideally be Thin. Medium or Slightly Thick or any combination of these grades (e.g. Thin - Medium or Medium - Slightly Thick).



Denotes changes in the structure of a stone which give it a 'smeared' impression under magnification. The term is generally only used for flawless stones and can reduce their value by up to ten per cent depending on the extent of the graining.



Read more about investment diamonds.



The Kimberley Process Certification Scheme (KPCS) was founded in 2003 as a system for verifying the origins of diamonds. It was founded in response to evidence in the late 1990s that warring factions were abusing trade in rough diamonds to finance their conflicts, and was designed to halt trade with these blood or conflict diamonds. 49 countries have signed up to the Kimberley Process, with the European Union counting as a single member. Members undertake to comply with strict rules and standards to ensure that all diamonds traded are of legitimate origin. (For detailed information on the Kimberley Process see






The lower part of a diamond or gemstone below the girdle.



Phosphorescent diamonds (including blue diamonds) emit red light when seen under ultra-violet light - and continue to do so long after the ultra-violet source has been removed; the length of this phosphorescent afterglow depends on the individual diamond.



A term used for setting of half-finished brilliants in tiny 'pots'. Pincetting is a specialist profession and requires as much skill and care as cutting itself.



A diamond must be extremely finely polished to ensure no traces of the cutting process are visible on the surface and all corners and edges are crisply defined. Polishing traces are almost always invisible to the naked eye but may impair the brilliance of a diamond to a very slight extent. Polish is graded in categories from Fair to Good, Very Good and Excellent. Symmetry and polish are key criteria in evaluating the quality of a cut.



For information on price trends for diamonds and their increases in value, see Diamond Prices.



Are you interested in rough diamonds? Where can rough diamonds be purchased? Find out more about rough diamonds.



Symmetry is the term used to describe the form of a diamond and the arrangement of its facets, which should be as uniform as possible. The quality of symmetry of a diamond impacts on its brilliance. The symmetry grade indicates whether the diamond has a regular and symmetrical cut. For example, the culet may not be in the exact centre of the diamond, or the facets on the upper part may not correspond exactly with those on the lower part.


The main criteria used to determine the symmetry of a cut diamond are:

  • Facets match each other exactly
  • All facets are symmetrical
  • Culet and table should be centred
  • The cut has additional facets or larger facets



The central flat surface at the top of faceted gems, and at the same time the largest facet of the top part of the diamond. The table percentage of a diamond gives the ratio between the table (the central top facet) of the diamond and the total diameter (table:width). A table percentage of between 57% and 62% is generally regarded as optimum. Larger or smaller proportions impair the brilliance of the diamond.  

Drawing of diamond with culet, girdle and table



Treated diamonds are natural diamonds subjected to subsequent enhancement processes to improve, say, their clarity or colour. A diamond is classified as untreated if it has only been altered from its natural state by cutting or polishing. Treated diamonds must be designated and clearly identified as such.


RenéSim will only supply treated (occasionally known as 'clarity enhanced') diamonds in response to specific enquiries. Our Diamond Search offers only untreated diamonds. The reason is easy to explain: treatment destroys the natural charm - the natural brilliance and sparkle - of a diamond. Treated diamonds are generally available at lower prices since their raw material is of lower quality. In our opinion, their long-term retention of value is extremely doubtful. For individual pieces of jewellery where budget and not quality is the primary concern, we recommend costume jewellery instead. Modern costume jewellery offers synthetic imitation diamonds created, like treated diamonds, under laboratory conditions, but at far more reasonable - and generally fairer - prices.


Treatment methods include:

  • Colour enhancement: Diamonds are heated to enhance their colour. A distinction is made between a process where the colour is inserted externally into the stone and a process of developing and deepening colours that already potentially exist within the stone.

  • HPHT method: In this radiation-free method, coloured diamonds (generally with a brown hue) are bleached under high temperatures (2300-2500° Celsius) and high pressure (around 65kbar).

  • Laser treatment: Small inclusions in the diamond are removed by laser.

  • Clarity enhancement: Diamonds are treated before or after cutting using various methods to enhance their clarity. This can be done by inserting colourless substances (e.g. oil, wax or resin) into cracks and cavities.

You may also be interested in the following:

Are you interested in purchasing diamonds as gems or investments? Search our diamond database for loose diamonds.

You can find premium quality diamond post earrings in the section Diamond Post Earrings, and diamond jewellery in the section Diamond Jewellery.

If your interest is in jewellery in general, browse the information in our Jewellery Lexicon or see our overview on diamonds: Diamond.

We have assembled all you need to know about gemstones in our Gemstone Lexicon.

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As an online jeweller, RenéSim combines the benefits of a modern online-based business model with 180 years of family-run traditional craftsmanship in the jewellery industry. Gemstones such as diamonds are the central focus at RenéSim; we supply high-quality, thoroughly individual pieces such as engagement rings in addition to loose diamonds. We offer unique diamond post earrings, diamond rings, memory rings, engagement rings and much more. Consult the jewellery experts at RenéSim!

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