Only 0.3% of all diamonds display a colour that is predominantly blue. Of this only a very small subsection qualifies as Fancy Vivid Blue. In a study comprising over 462 blue diamonds, the Gemmoligical Institute of America (GIA) graded merely 1% as Fancy Vivid Blue. The Monograph, created especially for The Mediterranean Blue, gave GIA the chance to share new scientific insights into the formation of blue diamonds. The GIA was able to establish that blue diamonds are formed far deeper in the Earth’s mantle than any other diamonds. Furthermore, the world-renowned laboratory also discovered an inherent link between blue diamonds and the oceanic waters.

Grading Blue Diamonds
Blue diamonds occur in a wide range of tones, but only in a relatively small range of saturation. As the grade boundaries are more nuanced than is the case for other coloured diamonds, longstanding experience is required to face the challenges of grading blue diamonds. The differences in tone can easily be misinterpreted as differences in saturation to the inexperienced eye.

Sources
The Mediterranean Blue was unearthed in South Africa as an impressive rough weighing 31.93 carats. It was subsequently fashioned into the present 10.03 carat cushion-shaped diamond.

From the 1860s onwards, South Africa emerged as the predominant source, not just of large and beautiful diamonds, but occasionally of rare fancy coloured diamonds as well. South African mines that are known to have produced blue diamonds include Jagersfontein and Koffiefontein, both of which were located near Kimberley. Smaller sources were also found at the Bellsbank mine near Barkly West and at the Helam mine in Swartsruggens. Very rarely, blue diamonds have been found in alluvial deposits at Lichtenburg in the Western Transvaal. Historically, central Africa has been a source, particularly the Congo and Angola. Other West African countries such as Guinea and Sierra Leone are also known to have produced blue diamonds. Outside of Africa, blue diamonds have also been discovered in Borneo.

Type IIb Diamonds
The Mediterranean Blue is a type IIb diamond which signifies that a small amount of the trace element boron is present in its chemical composition. Boron in turn contributes strongly to the blue appearance of the diamond, which is also related to exposure to high pressure during the formation process. An unusual property of type IIb diamonds is their high electric conductivity.

Boron and Oceanic Crustal Subduction
Boron is a chemical element that is concentrated in rocks and sediments near the Earth’s surface. When these crustal rocks weather and decompose, boron is filtered into rivers where it is delivered as dissolved chemical elements into the ocean. In mantle rocks, however, the concentration of boron is very low.

Recent scientific studies suggest that boron, incorporated in clays and other minerals in the oceanic crust, is carried down into the mantle along with hydrous minerals by a conveyor-like-process which is called oceanic crustal subduction by geologists. In the mantle, these crustal minerals break down and release a boron-rich fluid that triggers diamond formation.

Formation
It is possible for geologists to age-date the formation of rough diamond crystals based on tiny amounts of radioactive mineral inclusions which get trapped in the growing crystals. It is now known that diamond formation began as much as 3.5 billion years ago, and the resulting crystals then remained deep in the earth for millions of years, before being emplaced near the earth’s surface in more recent geological times.

Most blue diamonds contain boron and little to no nitrogen, they display an irregular crystal lattice and can sometimes occur in large sizes. These features suggest formation under different geologic conditions compared to the majority of colourless diamonds. Blue diamonds can also contain mineral inclusions which allow geologists to deduce information on the depth and host rock during the diamond’s formation. The minerals encountered within these inclusions are only found together in environments exposed to high pressure, extremely deep inside the Earth’s mantle.

These mineral inclusions allow scientists to conclude that blue diamonds formed at a depth of 400 to 600 kilometers within the Earth’s mantle. In contrast, the majority of near-colourless diamonds were created between 150 and 200 kilometers below the Earth’s surface and resided there for millions of years before volcanic eruptions emplaced them near the Earth’s surface. Therefore, blue diamonds are formed much deeper within the Earth’s mantle than the vast majority of other diamonds.

Crystal Structure
Intense pressure on the diamond’s crystal lattice during formation causes strain, which can be detected as patterns of bright interference colours when viewing a diamond under high magnification under polarizing filters. When strain is present in the diamond’s structure, patterns of bright interference colours will appear. These patterns correspond with the host structure of the diamond and are indicative of internal stress and distortion during the diamond's formation. This distortion of the crystal lattice enhances the depth and strength of the blue hue.

Under cross-polarized light, The Mediterranean Blue displays a type of strain known as cross-hatched or “tatami” strain, commonly seen in type IIb diamonds.

Conclusions of the Monograph
The Monograph, created especially for The Mediterranean Blue, contains new scientific insights into the properties and genesis of blue diamonds, which set them firmly apart from any other kind of diamond. Due to the presence of strain and the types of mineral inclusions encountered, blue diamonds appear to have formed much deeper inside the Earth’s mantle than any other diamonds. Furthermore, the element boron which is primarily responsible for the blue colour, is rarely present in the Earth’s mantle. Instead, it occurs in clays in the oceanic crust and is subsequently transported to the Earth’s mantle by oceanic crustal subduction. Therefore, The Mediterranean Blue’s colour is inherently linked to the world’s vast, mysterious and devastatingly beautiful oceans.

Cutting The Mediterranean Blue
The Mediterranean Blue was mined in South Africa as an impressive rough weighing 31.93 carats. After careful planning, followed by a cutting process that lasted well over half a year, The Mediterranean Blue was fashioned as a cushion modified brilliant-cut diamond weighing 10.03 carats. The process of preforming, blocking and polishing The Mediterranean Blue was fully documented in photographs, forming a unique documentary record of this exceptional blue diamond’s conception.

The cutting process for blue diamonds is not analogous to near-colourless diamonds, or any other coloured diamonds for that matter. Blue diamonds usually occur as irregular, asymmetrical crystals. The blue colour may also be unevenly distributed throughout the rough crystal. Therefore, careful study of the crystallographic directions of the rough, and the properties of the stone, are needed to bring out the full potential of its colour and overall appearance. A high level of experience and expertise are therefore needed to cut and polish a blue diamond.

To achieve the best possible visual appearance, expert diamond cutters often make modifications to traditional cutting styles. Selecting a cushion-shaped outline reminiscent of many historical diamonds, such as the Régent and Cullinan II diamonds, the cutter placed the gem in an ongoing dialogue with these storied gems of yesteryear, whose timeless appeal has never ceased to mesmerise each successive generation of admirers. The diamond’s Vivid Blue colour is perfectly offset by its classic, elegant cushion-shape with harmoniously softened edges.