Although the diamond is the hardest gem known to man, its composition is a simple one:  it is common carbon, like the graphite of pencils, but with a structure that involves a fusion point of 6900 degrees Fahrenheit, that is two times the fusion point of steel. Billions of years ago the elementary forces of heat and pressure transformed carbon into diamond. The volcanic mass in which this crystallization happened increased and came through the land crust cooling itself in the kimberlitic fireplaces. It is in fact in these kimberlitic fireplaces that diamonds are still found today

  Selezione diamanti ad Anversa

The 4 C's of diamonds

There are 4 main characteristics to be taken into consideration for a correct appraisal of a diamond:


All four, or importantly their combination, confer to a diamond their uniqueness and determinate internationally a fair market value.
Following is a brief description of how these characteristics and how they effect the value of precious stones.


The colour of a diamond is perhaps its most appreciable characteristic, also to eye. The more the diamond is white and more light can be reflected crossing it. Obviously this quality greatly affects every stone’s value determining the price of a diamond. 
A diamond of colour  H  or  G  (that is with an optimal white colour) can  cost up to  50% more than a stone of  I colour other characteristics  being equal (cut, carats and purity). The appraisal of the colour of a diamond is extremely difficult and is carried out with the aid of coloured stones called “comparison stones”.
Various scales of appraisal of the colour of diamonds exist, one of the most used is the GIA scale ( 
Gemological institute of America ) that we summarize as follows.

GIA diamond colour scale grade

diamante colore d e f
colore diamante g/h
colore diamante i/j/k
diamante colore l m n
diamante colore o p
diamante colore q r
diamante colore s z
  D E F G H I J K L M N O P Q R S==> Z
Exceptional White Rare White Slightly Tinted White Tinted White
Tinted Coloured

18Carati uses only G colour Vs clarity diamonds.


The cut of a diamond represents in the last analysis the ability of a stone to reflect light in an optimal way and it determines therefore the brilliance. It is a common mistake to confuse the cut with the shape (which we talk about later). The most common shape is without a doubt "the brilliant cut", that is of round shape on the top. When observing  an ideally cut stone, the light enters from the top part of a diamond as refracted to straight angle the in order to leave  from the same part giving  the stone a remarkable brightness and "brilliance" (see diagram): The classic brilliant cut comprises 58 facets 33 of which located on the top part (or crown) and 25 on the bottom part (or pavilion). When the crown represents a third of the total height of the diamond, the best brilliance is obtained.

Diamond proportions diamond crown Taglio ideale del diamante
  • A - Crown
  • B – Upper angle 34’ lower 41’
  • C - Culet
  • D - Total depth 61.7%
  • E - Table 55 - 57%
  • F – Girdle diameter
  • G – Lower girdle
  • H – Main pavillon
  • I - Pavillon 43%
  • A - Upper girdle
  • B – Girdle
  • C - Table
  • D - Star
  • E - Bezel
  • F – 100 %
  • G – 55 - 57%
The Ideal Cut


Different types of diamond cut
taglio tondo detto anche brillante Taglio princess quadrato Taglio smeraldo Taglio radiant Taglio ovale Taglio goccia (o pear) Taglio marquise (navetta)


The purity of a diamond is an important factor when determining the value. Diamonds without inclusions, that is totally without punctiform imperfections inside that are visible with 10X magnifying glass are real rarity.
Small imperfections called inclusions are very common. The smaller the inclusions (or their absence) determines how precious and valuable our stone will be.
It goes without saying that the differences in purity between similar stones are much difficult to establish by a layman and only a gemologist, with the aid of special white light and magnifying glass,  is able to establish if a diamond is  a Vvs2  (Very very small inclusions) rather than a Vs1  (Very small inclusions). To the eyes of layman they can appear identical when in fact there are remarkable differences in value.
For this reason it is always advisable to purchase diamond jewellery from trustable and expert traders. Always ask to know the characteristics of the diamond that you wish to acquire.

GIA - Diamone Purity Scale
Diamante flawless - completamente puro alla lente Diamante VVS1 Diamante VVS2 Diamante VS1 Diamante VS2
F Flawless VVS1 Very Very Small Inclusions VVS2 Very Very Small Inclusions VS1 Very Small Inclusions VS2 Very Small Inclusions

diamond has no external or internal inclusions of whatever type under a 10X
magnifier lens

The diamond contains of the minimal inclusions extremely difficult to find under a 10X magnifier lens

The diamond contains minimal inclusions barely identifiable under a 10X magnifier lens

The diamond  contains some observable inclusions which are not easily visible under a 10X magnifier lens

The diamond contains some noticeable inclusions visible under a 10X magnifier lens

Diamante SI1 Diamante SI2 Diamante I1 piquè Diamante I2 piquè Diamante I3 piquè
SI 1 Small Inclusions SI 2 Small Inclusions I 1 Piquè I 2 Piquè I 3 Piquè

The diamond contains easily seen inclusions and/or characteristics with a 10 X magnifier lens

The diamond contains inclusions and/or characteristics easily seen visible under a 10X magnifier lens

The diamond contains obvious inclusions and/or very visible characteristics under a 10X magnifier lens

The diamond contains easily visible obvious inclusions

The diamond contains obvious  inclusions which are very easily visible



When talking about diamonds (or more in general of precious stones) the carat is simply the unit used to  measure its weight and is equivalent to a fifth of gram (0,20 grams). Be careful not to confuse the carat meaning the measurement of the purity (or fineness) used in precious metals such as gold or platinum which we will speak about later.
The carat, generally abbreviated in  Ct. ,  constitutes the measurement of the  weight of a precious stone. In the following table, we give approximate dimensions of round cut diamonds (called brilliant cute), which corresponds to given carat value.

The carat of a stone is also important in determining its value and not only because obviously the value increases as the carat increase, but also because bigger stones cost much more than the equivalent weight made of smaller stones. That means for instance that a one carat single stone (Ct. 1.00) is a lot more valuable then 100 stones of 1 point of a carat (Ct. 0.01).
Referring to the carat of diamonds “points” are  often mentioned; The point of carat is the hundredth part of the carat (= 0,002 grams) and it is often used for weighing of very small diamonds .


Diamante SI2