Blue diamonds are among the rarest of all coloured diamonds. Originally mined in India’s famed Golconda mine, blue diamonds are currently mined in Australia and South Africa, and can cost as much as $100,000 to $250,000 USD per carat, depending on colour, clarity and carat weight.
No other colour of diamond has so much superstition associated with it. The Hope Diamond, a 45.52ct natural vivid blue diamond that currently resides in Washington D.C.’s Smithsonian Institute, is said to be cursed, as a disproportionate number of its previous owners have experienced ill fates after the diamond came into their possession. It is said to glow eerily when exposed to ultraviolet light, an element that has only added to the mystery surrounding this diamond.
The blue colour in natural diamonds is caused by boron, a naturally occurring mineral. The concentration of boron in the area where diamonds are mined will contribute to the intensity of the colour in a blue diamond, increasing its market price accordingly. The Gemmological Institute of America (GIA) grades natural blue diamonds on the following scale from lightest to most intense: faint blue, very light blue, fancy light blue, fancy blue and fancy dark blue. The Hope Diamond is considered a fancy dark blue diamond.
Like many coloured diamonds, natural blue diamonds are extremely rare and are much more expensive than white diamonds. Colour enhanced or colour treated diamonds are diamonds that have been colour enhanced to create a variety of colours, including blue. These diamonds are much more readily available, and are much more affordable than naturally occurring blue diamonds. If you are interested in a natural blue diamond, ensure that your diamond comes with a certificate from a reputable diamond certificate laboratory, such as GIA, declaring it to be a natural blue diamond.
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Natural blue diamonds are more expensive than colourless diamonds, how much more expensive depends on the intensity of the blue colour. The famous Hope Diamond is a deep royal blue and is one of the most valuable diamonds ever found. Blue diamonds can also be artificially coloured by applying high pressure, high temperature treatment (HPHT) to brownish-coloured diamonds. These treated blue varieties are significantly less valuable than colourless diamonds.
There are several factors to consider when determining the value of a blue diamond. Natural blue diamonds are extremely rare and expensive whereas treated blue diamonds are less valuable than colourless diamonds. In natural blue diamonds, the intensity of the colour has a significant impact on the price. Blue diamonds can occur naturally in pale, icy blue colours through to deep royal blue hues. The more intense the colour, the more valuable the diamond.
Natural blue diamonds are extremely rare, the mines that have unearthed the most blue diamonds are located in South Africa, Western Australia and India.
Natural blue diamonds around the 1 carat weight usually go to auction. After red diamonds, blue diamonds are the most valuable coloured diamonds on earth. Historically they have fetched prices up to 80 times that of a similar sized colourless diamond. In September 2018, the 12.03ct Blue Moon of Josephine Diamond sold at auction for over $48.4 million dollars.
Blue diamonds can occur naturally where boron is present and trace amounts become part of the chemical composition. Blue diamonds can also be created artificially by irradiating brown diamonds or treating them with HPHT (high-pressure, high-temperature).