The most important quality characteristics that determine a diamond's value are the 4 Cs.

 

Carat – Weight

Describes the diamond's weight.

1 carat = 0.2 grams.

Larger carat numbers generally mean higher prices – but even small diamonds can be very valuable if the other Cs are right.

 

Cut – Sparkle & Brilliance

Determines how well the diamond reflects light.

A good cut makes the diamond shine and sparkle – regardless of size or color.

 

Clarity – Internal and external characteristics

Evaluates how many small inclusions (impurities) are present in the diamond.

The purer the stone, the rarer and more valuable it is.

 

Color – Diamond color grade

Diamonds are most valuable when they are colorless (white).

The scale ranges from D (high-quality colorless) to Z (visibly yellowish).

 

Memory tip:
Cut, color, clarity, and carat together determine the value and beauty of a diamond. A perfect diamond is therefore not only large, but also brilliantly cut, pure, and colorless.

Diamonds form deep within the Earth's mantle under extreme pressure and temperature conditions. The majority of gem-quality diamonds originate at depths ranging from 150 to 200 kilometers (approximately 93 to 124 miles) beneath the Earth's surface.  

 

These depths correspond to the base of the oldest and thickest parts of continental lithosphere, known as cratons, where conditions are stable enough for diamond formation over billions of years. 

 

In addition to these, a smaller subset of diamonds, referred to as "superdeep diamonds," form at even greater depths within the Earth's mantle. These can originate from depths of 300 to 800 kilometers (approximately 186 to 497 miles), encompassing regions such as the mantle transition zone and the lower mantle.  The formation of these diamonds occurs under even more extreme conditions and provides valuable insights into the deep Earth's composition and processes.

 

It's important to note that while diamonds form at these significant depths, they reach the Earth's surface through rare and violent volcanic eruptions, specifically via kimberlite and lamproite pipes. These eruptions rapidly transport diamonds from the mantle to the surface, preserving their structure during the ascent. 

The kimberlite and lamproite vents act as "elevators" that transport diamonds from the depths to the surface. These volcanic eruptions are extremely rapid and explosive, which is necessary to transport the diamonds without them converting to graphite.

Diamonds sparkle because they reflect light in a special way.

 

Each diamond has many flat, smooth surfaces (facets) that act like tiny mirrors. When light hits these surfaces, it is deflected multiple times inside and bounces from surface to surface. After several such reflections, the light exits the diamond and reaches our eyes – creating the bright, sparkling points of light.

 

Many smooth surfaces (facets): Diamonds are cut to have several small, smooth surfaces. Each surface acts like a small mirror that reflects rays of light.

 

Specular reflections: Inside the diamond, the light bounces from surface to surface like a hall of mirrors and is repeatedly reflected back. Only after several such redirections does the light leave the stone.

 

Luminous points of light: Due to these multiple mirror reflections, you see many bright flashes of light when looking at the diamond. When you move the diamond, the points of light constantly change, creating the characteristic sparkle.

 

Colorful rainbow colors: A diamond can split incident white light into its rainbow colors.

 

This is why diamonds often sparkle in many colors—a play of colors known as the diamond's "fire."

Mohs hardness is a scale from 1 (very soft) to 10 (very hard) that indicates how resistant a mineral is to scratches. Harder materials scratch softer ones – if mineral A scratches mineral B, then A is harder than B.

 

Diamond ranks at the top with a Mohs hardness of 10, making it the hardest known mineral. This means: A diamond can scratch all lower hardness grades, but nothing can scratch the diamond itself.

 

For comparison: Quartz (for example, rock crystal) has a Mohs hardness of 7 and easily scratches glass (window glass ≈5.5). Normal glass is around 5–6, and steel around 4–5 on the scale. These materials are therefore significantly softer than diamond.

 

A diamond can easily scratch glass or steel, while conversely, glass and steel do not damage the diamond. This shows why diamond is often considered the hardest material of all.

Many people mistakenly use the term "brilliant" as a synonym for diamond – but this is incorrect.

 

A diamond is a naturally occurring mineral composed of pure carbon. It is the hardest known material and is valued for its brilliance and rarity.

 

A brilliant, however, is not a separate type of gemstone, but rather refers to a specific cut – the so-called brilliant cut.

 

Other gemstones can also be cut in a brilliant cut.

 

In short:

Diamond = the material
Brilliant = the cut

 

Not every diamond is a brilliant. And not every brilliant is a diamond.

 

This confusion is widespread – but a clear mistake for experts.

Depth and Conditions: Diamonds form at depths of approximately 150 to 200 kilometers below the Earth's surface, where temperatures of at least 1000°C and pressures of 40 to 60 bar prevail.

 

Source Material: The starting material is pure carbon, which crystallizes over long periods of time under these extreme conditions and takes on the characteristic cubic structure of the diamond.

 

Age: Most natural diamonds are over a billion years old.

An unpolished area, typically at a facet junction, that appears as a white scratch, often due to wear.

Rudimentary digging at the surface of alluvial deposits by individual diggers using simple tools. Artisanal diggers are vulnerable to those who would prey on them. The Diamond Development Initiative is specifically designed to help artisanal miners.

An ASET image (Angular Spectrum Evaluation Tool) is a special analytical image that visualizes a diamond's light performance. Developed by the American Gem Society, it serves as a visual guide for objectively assessing and comparing a stone's brilliance, fire, and optical beauty.

The main facets of the crown.

A preliminary step in diamond cutting where the basic proportions and symmetry of the diamond are established and the first 8 facets on both crown and the pavilion are placed.

The effect created by light return as a result of a combination of brightness and positive contrast.

Cutting style that features vertical triangular or kite-shaped facets that radiate from the center. The round brilliant and princess cut are examples of this facet style which results in a much different ‘flavor’ than step cuts featuring prominent horizontal facets.

The process of cutting the final forty facets on the diamond including the upper and lower girdle and star facets.

A unit of weight: 1.00 carat = .20 grams. Carat weight is widely equated to diamond size, however diamonds can have exactly the same weight and significantly different dimensionality, depending on cut proportions.

Common term for a gemological laboratory report.

The degree to which a diamond has internal inclusions and external blemishes. Laboratory clarity grading is done by trained graders and assessed at 10X magnification.

A thin layer of synthetic diamond over a non-diamond material designed to defeat certain types of diamond testers and/or to give a material better resistance to scratching.

Refers to body color. Diamonds in the normal range are graded D-Z depending on how much body color they exhibit, usually yellow or brown. Laboratory color grading is done by carefully comparing the diamond against known master sets of diamonds.

Diamonds illicitly obtained and involved in fueling conflict between militant groups and legally established governments. The Kimberley Process was instituted in 2002 to stem the flow of conflict diamonds.

The differential brightness between adjoining facets which contributes to the perception of brilliance, fire and scintillation.

The part of the diamond above the girdle.

The angle created by the interface between the girdle and the bezel.

The measurement from the belt to the table top.

The tip of the pavilion. It can be pointed or have an additional facet varying in size from very small to large.

Aspects of the proportioning and polishing of the finished diamond. Light performance and beauty are impacted more by cut quality than any other aspect. Sometimes ‘cut’ is also used in reference to the shape, e.g. emerald cut.

The measurement extending from the table to the culet.

The depth of the diamond expressed in relation to the average diameter. (total depth/diameter)

The prismatic separation of white light into its individual color components as a result of refraction. The resulting colored sparkles produced by the crown are referred to as Fire.

A slightly scaled down GIA document for diamonds under one carat. The report does not include a stone plot but the diamond is laser inscribed for identification purposes.

A flat polished surface on a finished gem.

Refers to diamonds with body color beyond the normal range (beyond Z). Fancy color diamonds have their own grading system.

Any non-round diamond is referred to as a fancy shape.

colored sparkles created by refraction and the dispersion of white light into its individual components.

The small vertical plane around the perimeter of the diamond. It can vary in thickness and can be faceted, polished or unpolished.

The pairs of facets below the girdle and between the pavilion mains.

The main facets that normally extend from the girdle to the culet on the pavilion and from the girdle to the table on the crown. The crown mains are also called bezel facets.

The portion of the diamond below the girdle.

The angle created by the intersection of the girdle and the main pavilion facet.

The small triangular facets between the table and the upper girdle facets.