Everything You Need to Know About Blue Diamonds

| 5 min read

Naturally coloured Diamonds are among the most valuable of all gemstones, and Blue Diamonds are one of the rarest. 

Few gemstones are more coveted than the Blue Diamond, and it is a stone adored by both Diamond lovers and jewellery enthusiasts worldwide. But how did it get its colour? And what makes it so remarkably rare? 

Understanding a subject can significantly influence our appreciation of it, so if you're looking to add something blue to your jewellery collection, here is everything you need to know about the unique treasure that is the Blue Diamond. 


Blue Diamonds

Of all the Diamond colours available, Blue Diamonds are among the rarest, with the odds of finding one in a mine being around 1 in 10,000. The traces of boron within its crystal structure results in its blue colouration, and its tone can range anywhere from a light pastel to a deep, vivid blue. 

Their striking beauty and scarcity make Blue Diamonds highly sought after among collectors and an ideal choice for luxury jewellery. Their alluring hue and exclusivity set them apart from their colourless counterparts, and their associations with purity, love and commitment make Blue Diamond rings perfect for proposals. 

Hope Diamond

This magnificent gem has also gained a lot of celebrity endorsement in its time, with glamorous women like Celine Dion and Kate Winslet seen wearing them on the red carpet. It is also said that the iconic 'Heart of the Ocean' necklace worn by Winslet in the 1998 film Titanic is inspired by the 45.52ct Hope Diamond, the most famous Blue Diamond in the world (pictured above). 


Natural Blue Diamonds form deep within the Earth, and the boron atoms absorb red and yellow light during this process, causing the gem to appear blue. However, this natural phenomenon is exceedingly rare, making natural Diamonds of this colour difficult to source and, therefore, expensive. 

Blue Diamond Gems

To combat the scarcity of Blue Diamonds, it is common for natural, earth-mined Diamonds to undergo a high-pressure, high-temperature (HPHT) process to alter their colour to blue.  

Here is a step-by-step guide to how the HPHT treatment works. 


Before treatment, the Diamond must be cleaned to remove any surface impurities. 

HPHT Conditioning 

The gem is then exposed to the pressures and temperature conditions that Diamonds face deep within the Earth's mantle, a process which is replicated in a controlled environment. 

Gemstone Lab

Element Introduction

The Diamond's crystal structure is then introduced to whichever chemical element is required for its colour. In this instance, boron atoms replace some of the carbon atoms inside the Diamond to alter its colouration.


After the desired colour is present, the Diamond is cooled in order for the new colour to stabilise. 

The HPHT process offers a much more affordable alternative for supplying the demand for coloured Diamonds. The treatment is non-reversible and does not affect the Diamond's value, as it will still test as a naturally mined gem. 


Blue Diamond

Without the HPHT process, thousands of Diamonds must be unearthed in order to find a naturally blue one, and they historically cost much more than colourless Diamonds of the same clarity and weight.

Plus, a rough Blue Diamond is rarely symmetrical and can have areas that are more blue than others; this makes a lapidarist's job extremely difficult when deciding how to cut and polish the stone to enhance its colour best.  

Overall, Blue Diamonds are highly prized and often demand a higher price than more common Diamonds of an equivalent or similar grade.


Large Blue Diamond

As we've mentioned, a Blue Diamond's distinctive colour derives from the presence of boron. However, boron is just the leading cause, as radiation, nitrogen and hydrogen can also contribute to the gem's unique tones.  

The nitrogen levels determine the intensity of the stone's blue hue; if nitrogen levels are low during the Diamond's formation process, the blue will be much richer. Additionally, Blue Diamonds with radiation exposure are often called green-blue, whereas stones associated with hydrogen are said to be more grey-blue. 


Cullinan Mine, South Africa

Very few places around the world produce natural Blue Diamonds, the most notable today being South Africa's Cullinan mine and the Argyle mine in Australia (although this mine closed in 2020).

Historically, India was a well-known source of the rare gem; in the 17th century, many were sourced in Golcondo Sultanate and brought to the West by gemstone dealer Jean-Baptiste Tavernier. He sold one of them to King Louis XIV of France, which earned it its original name: the 'Tavernier Blue'. Soon after, this Diamond was recut into the French Blue that first appeared in the French crown jewels — but it was stolen in 1792 and had to be recut.  

But, with all that said, the most infamous Blue Diamond ever found continues to be the 45.52ct Hope Diamond. 


Blue Diamond Stone

With its unique hue and scarcity, the Blue Diamond remains one of the world's most captivating and sought-after gemstones. Its rare beauty and storied past have fascinated gemologists and jewellery enthusiasts for years, and provide an incomparable glimpse into the extraordinary treasures our planet has to offer.

Due to their extreme durability and symbolism, Blue Diamonds are perfect for rings. To find your next piece, explore our selection of Blue Diamond rings here. But if blue isn't your colour, why not explore the rest of our Diamond jewellery, including our vast array of Coloured Diamonds?

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