Raphaelle Godfrey, Head of Jewellery at Chiswick Auctions and a qualified gemmologist, shares expert insight into what makes diamonds so prized and why they continue to hold their value.
Natural diamonds are between 1 and 3.5 billion years old. They are formed deep within the Earth’s mantle under extreme pressure and temperatures of around 1,000°C. While diamonds are composed of carbon, just like graphite (the material found in pencils), their structure is entirely different. It is this crystalline structure that gives diamonds their exceptional hardness and brilliance.
Diamonds rank 10 on the Mohs scale of hardness, making them the hardest known natural substance. Only another diamond can scratch a diamond.
Extracting diamonds is also a complex and expensive process. Whether mined from pipes, rivers or the seabed, the equipment and processes required are substantial. Once mined, only around 20 percent of diamonds are suitable for use in jewellery. The remainder are used for industrial purposes.
The value of a diamond is traditionally assessed using the internationally recognised Four Cs:
Carat – The weight of the diamond. One carat equals 0.2 grams.
Colour – The degree to which a diamond is colourless (graded from D to Z), or the presence of a desirable fancy colour.
Cut – The way the diamond has been shaped and faceted to reflect light and maximise its brilliance.
Clarity – The presence (or absence) of natural inclusions or blemishes within the stone.
There is also a fifth 'C' that plays an important role:
Certification – A report from a recognised gemmological laboratory, verifying the diamond's characteristics.
The pricing of diamonds is not linear but exponential. A small increase in size, clarity or colour grading can result in a significantly higher value. For example, moving from a 0.90 carat to a 1.00 carat diamond can mean a noticeable jump in price.
This is why it is important to understand which characteristics matter most to you when selecting a diamond, so you can make the best decision for your budget without compromising on quality.