Diamonds: Characteristics, Meaning, Jewellery and the 4 Cs

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The diamond is the world’s best-known gemstone and the classic symbol of engagement jewellery. In this guide, you’ll learn about the characteristics of diamonds (composition, hardness, brilliance), the significance of the stone, how it features in jewellery, what the 4 Cs are (carat, colour, clarity and cut) and how to recognise a real diamond. At the end, there is an FAQ section covering the most common questions.

The name comes from the Greek adamas, which can be translated as ‘unchanging’ or ‘indomitable’. As the idea of ‘indestructible’ is often repeated, it is worth noting that whilst a diamond is extremely hard, it can chip or break with a single blow, as you will see below.

Os diamantes são usados principalmente em joias, embora também tenham aplicações industriais importantes. — Diamonds are mainly used in jewellery, although they also have important industrial applications.

What is a diamond?

A diamond is a crystallised form of carbon, which is arranged in a cubic lattice. Natural diamonds are formed in the Earth’s mantle, at a depth of around 150 to 250 km, and most are between 1 and 3.5 billion years old. Volcanic eruptions have brought these stones close to the surface, and today they are extracted from rocks such as kimberlite or from river deposits (alluvial deposits).

Pedras de Diamante Lapidadas — Cut Diamond Stones

A rough diamond usually looks opaque or dull, quite unlike the ones seen in shop windows. The brilliance we are familiar with only appears after it has been cut. There are also laboratory-grown diamonds, which have the same chemical composition and structure as natural ones (see the section on them below).

Properties of the diamond

Composition: crystallised carbon. Small amounts of other elements, such as nitrogen and boron, alter the colour of the stone;
Natural origin: formed under high pressure and high temperature in the Earth’s mantle, at a depth of around 150 to 250 km;
Density: from 3.5 to 3.53 g/cm³;
Hardness: 10 on the Mohs scale, the highest rating. Only another diamond can scratch a diamond;
Toughness: hardness is not the same as impact resistance. Diamonds have cleavage planes and can chip or break on impact, and gem cutters use this to split the rough stone;
Brilliance and dispersion: the refractive index is high (around 2.42) and the dispersion (0.044) is also relatively high, which produces the ‘fire’ that separates light into colours once the stone has been cut properly.

Tabela de dureza de mohs — Mohs hardness scale

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Como identificar um diamante

The meaning of the diamond

The meanings associated with diamonds stem from tradition and culture, rather than scientific evidence. The most common interpretation links the stone to eternity, purity, strength and commitment, precisely because of its hardness and brilliance. This is why it is the most commonly used gemstone in wedding and engagement rings.

A few key events help to explain this fame:

Engagement ring: the first well-documented diamond engagement ring dates from 1477, when Archduke Maximilian of Austria presented one to Mary of Burgundy. The custom became widespread in the 20th century, following De Beers’ advertising campaigns from 1938 onwards, and the slogan ‘a diamond is forever’ dates from 1947 (source: Wikipedia);
April’s birthstone: the diamond is the traditional birthstone for those born in April;
Diamond wedding anniversary: marks 60 years of marriage.

Diamonds in jewellery

In jewellery, diamonds are found in engagement rings, wedding rings, earrings, necklaces and bracelets, almost always set in gold or platinum. The value of a piece depends on the quality of the stone (the 4 Cs, explained below) as well as the metal and the jeweller’s craftsmanship. Here are some practical tips:

Always ask for a certificate from a gemmological laboratory (such as the GIA) for higher-value stones and check that the report number matches the stone;
Ask whether the diamond is natural or lab-grown, and whether it has been treated (for example, with colour treatment);
Remember that maximum hardness does not mean invulnerability: a blow from the side can chip the stone, especially at the edges (the ‘girdle’);
Compare the set as a whole, not just the size: two stones of the same weight can vary greatly in price.

The 4 basic diamond grading criteria: the 4 Cs

To make it easier to buy and compare gemstones, the GIA (Gemological Institute of America) developed the ‘4 Cs’ system, which is now the world’s best-known standard for evaluating natural diamonds. The four factors are:

Carat (weight in carats);
Color (cor);
Clarity (purity);
Cut (cutting or polishing).

Understanding the 4 Cs helps you shop with greater confidence and compare diamonds from different suppliers.

1. First C: Carat (weight)

A carat is a unit of weight (not size) and is equivalent to 200 milligrams, or 0.2 g. Each carat is divided into 100 ‘points’, so a 30-point diamond weighs 0.30 ct. A 1-carat diamond therefore weighs 0.20 grammes.

With the same type of cut – such as the brilliant cut, for example – a higher carat weight usually means a larger stone. However, two stones of the same weight can vary considerably in value, because colour, clarity and cut also affect the price.

Peso (quilate) e tamanho do diamante — Assuming the same type of cut – for example, the ‘Brilliant’ cut – the greater the weight (carat), the larger the stone will be.

2. Second C: Colour (cor)

To facilitate communication between buyers and sellers, the GIA has created a colour scale ranging from the letter D (colourless) to Z (visible yellowish or brownish tint). The assessment is carried out with the stone turned upside down, under controlled lighting, and compared with reference stones. The less colour there is, the higher the grade, and generally the higher the price.

Classiicação de cores de diamantes — Diamond colour grading

The groups in the GIA scale are:

D to F: colourless (D being the highest grade, with absolutely no colour);
G to J: almost colourless;
K a M: cor leve (faint);
N to R: very light to barely noticeable colour;
S to Z: visible colour (light), with a yellowish or brownish tinge;
Fancy: diamonds with intense natural colours (such as pink, blue, yellow or green) fall outside the D to Z scale and are classified under a separate system, that of ‘fancy colours’.

Coloured diamonds: what causes each colour

Yellow: nitrogen is the most common impurity in gem-quality diamonds and is responsible for their yellowish hues;
Blue: comes from the element boron, which replaces carbon atoms;
Red: is the rarest colour. In some red (and possibly pink) diamonds, the colour is attributed to a deformation of the crystal structure, rather than to an impurity;
Rosa: The Argyle mine in Australia became famous for these diamonds and ceased production on 3 November 2020, which has sparked increased interest in pink diamonds.

3. Third C: Clarity (purity)

Clarity (clarity) measures inclusions (internal characteristics) and surface defects (blemishes) that affect appearance and value. In Brazil, these marks are known as jaça. The GIA assesses the number, size, position, nature and prominence of these marks using a 10x magnifying loupe.

The GIA scale has 11 grades, ranging from the purest to the most included:

FL (Flawless): no inclusions or defects visible at 10x magnification. This is the highest grade;
IF (Internally Flawless): no inclusions visible at 10x magnification, but with minor surface imperfections;
VVS1 and VVS2: inclusions so small that they are difficult to see even for a professional;
VS1 and VS2: small inclusions, which require some effort to see with a magnifying glass;
SI1 and SI2: inclusions visible under a magnifying glass;
I1, I2 and I3: obvious inclusions, which may affect the stone’s transparency, lustre and durability.

Grau de pureza do diamante — Diamond clarity grade

4. Room C: Cut (cutting or polishing)

The cut refers to the quality of the cut, and should not be confused with the shape of the stone (round brilliant, oval, navette, pear, heart and others). It defines how much light a diamond reflects: brilliance (reflected white light), fire (light broken down into colours) and scintillation (the play of light and dark areas as the stone moves). The GIA also considers the proportions (angles, depths, weight-to-diameter ratio, durability) and the finish (symmetry and polish).

The GIA’s cut grading scale ranges from Excellent, Very Good, Good, Fair to Poor. Important: this cut grade is only awarded to round brilliant-cut diamonds, which are the only ones with a defined facet pattern. Shapes such as oval, marquise, pear, emerald or heart do not receive a GIA cut grade.

Many jewellers consider the cut to be the most important of the ‘C’s’ when it comes to a stone’s beauty, because a good cut reflects more light back to the viewer’s eyes. As the relative importance of the four factors depends on each buyer’s taste and budget, it is worth seeing the stone in person before making a decision.

Corte ou Lapidação no Diamante — Diamond Cutting or Polishing

The better the cut, polish, symmetry and cut of the diamond, the better the light return and, generally speaking, the higher the value.

Quanto melhor o corte, lapidação, simetria e polimento do diamante, melhor o retorno de luz — The better the diamond’s cut, polish, symmetry and brilliance, the better the light return

Tipos de Lapidação de Diamantes — Types of Diamond Cut

How to identify a real diamond

It is important to be able to identify a genuine diamond, as there are many imitations (cubic zirconia, moissanite and glass) and lab-grown diamonds. There are some tell-tale signs, but no home test can provide absolute certainty:

1. Teste do bafejo (fog test)

The idea is to let the air flow over the stone, as if it were a mirror. As diamond disperses heat well, the mist would tend to clear more quickly. But this test is not reliable: humidity, distance and temperature affect the result, and moissanite also conducts heat well.

2. Check the metal and the markings

Real diamonds are almost never set in base metals, such as stainless steel. Look for hallmarks indicating precious metal on the inside of the jewellery, such as 10K, 14K, 18K, 585, 750, 900, 950, PT or Plat. If you find ‘CZ’ (for cubic zirconia), the stone is probably not a diamond. But please note: the presence of a precious metal does not prove that the stone is a diamond; it merely reinforces the authenticity of the piece.

3. Examine the shine with a magnifying glass

Use a 10x magnifying glass and good lighting. In stones such as moissanite, you may notice double refraction (the facets appear doubled), something that diamonds do not exhibit. Very exaggerated coloured reflections may also indicate a fake, but a well-cut diamond also displays ‘fire’ in colours, so this alone is not a decisive factor.

4. Take it to a jeweller or gemmologist

The safest method is to take the jewellery to a jeweller or gemmologist, who will use instruments such as a loupe, a microscope and a thermal conductivity tester. For more valuable stones, ask for a laboratory certificate, such as one from the GIA. Inclusions help the professional to recognise natural stones, but not every imitation is too perfect, and not every natural diamond is flawless, so do not treat this as a hard and fast rule.

Natural diamonds and lab-grown diamonds

Lab-grown diamonds have the same chemical composition and the same crystal structure as natural diamonds. The two most commonly used methods are HPHT (high pressure and high temperature, starting with a diamond seed) and CVD (chemical vapour deposition, using carbon-rich gases). It is not an imitation like zirconia: it is a diamond, but of a different origin, and is usually cheaper. For the buyer, the important thing is that the origin is clearly stated.

In June 2025, the GIA announced that it would no longer use the colour and clarity scales for lab-grown diamonds, which will now be issued with a quality assessment report bearing the classification ‘premium’ or ‘standard’. According to industry press reports, the change came into effect on 1 October 2025, whilst the classification of natural diamonds remains unchanged. Always check the type of report for the stone you are buying.

Diamonds in Brazil

Diamonds were first discovered and mined in India, and it was in Brazil that the first diamonds outside India were found, in 1725, which subsequently led the country to overtake India as a source of diamonds. The Diamantina region, in Minas Gerais, is directly linked to this history, and the town has been a UNESCO World Heritage Site since 1999. In Bahia, the Chapada Diamantina also became known for its diamond mining. To find out more, read The Fascinating History of Diamond Mining in the Chapada Diamantina.

Sources consulted

Frequently Asked Questions

What does the word ‘diamond’ mean?

It comes from the Greek adamas, which can be translated as ‘unchangeable’ or ‘indomitable’. The word suggests resilience, and the diamond is indeed the hardest natural mineral (10 on the Mohs scale), but it can chip on impact.

What is the significance of the diamond?

Traditionally, the diamond is associated with eternity, purity, strength and commitment. It is the classic stone for engagement rings, the birthstone for April and the stone that symbolises the 60th wedding anniversary. These meanings are cultural and have not been scientifically proven.

What are the main characteristics of a diamond?

It is composed of carbon crystallised in the cubic system; it has a hardness of 10 on the Mohs scale, a density of 3.5 to 3.53 g/cm³, a high refractive index (around 2.42) and relatively high dispersion, which gives it brilliance and fire once cut.

What are the 4 Cs of a diamond?

These are the four factors used by the GIA to evaluate a natural diamond: carat (weight in carats), colour (colour, from D to Z), clarity (clarity, from FL to I3) and cut (cut, from excellent to poor).

How much does 1 carat of diamond weigh?

One carat is equal to 200 milligrams, or 0.2 grams, and is divided into 100 points. A carat measures weight, not size.

What is the best colour for a diamond?

On the GIA scale, grade D is colourless (the highest), and the scale goes up to Z, with a visible yellowish or brownish tint. Diamonds with intense natural colours, such as pink or blue, are classified separately as ‘fancy colours’.

Can a diamond break?

Yes. It is very hard and only another diamond can scratch it, but it has cleavage planes and can chip or break with a blow. That is why care should be taken with the edges, and it is best to seek advice from a jeweller.

Does the breath test work to determine whether a diamond is real?

It is not reliable. Humidity, distance and temperature can affect the result, and moissanite is also a good heat conductor. The safest option is to have it assessed by a jeweller or gemmologist and, for valuable stones, to obtain a laboratory certificate.

Is a lab-grown diamond a real diamond?

Yes, it has the same chemical composition and structure as the natural variety, but it has been produced in a laboratory (using HPHT or CVD). It is usually cheaper, and the seller must clearly state its origin.

How long does it take for a diamond to form in nature?

Natural diamonds were formed over billions of years: most are between 1 and 3.5 billion years old and originated at a depth of around 150 to 250 km, from where they were brought to the surface by volcanic eruptions.

Written by Willy Sievert

Editor of Bahia.ws since its founding in 2009. Based in Salvador, he travels frequently across the Northeast and all of Brazil to keep the guides up to date. Learn more about Willy Sievert →

Published on 11/02/2023 · Updated on 09/10/2026