While many of the basics of buying a diamond apply to all diamond types, they vary a bit among the different colours. Such is the case with natural purple diamonds, which are one of the rarest and most expensive in the family of fancy colour diamonds.
What Are Purple Diamonds?
Natural purple diamonds are among the rarest of the fancy colour diamond family. Few have been documented in the literature, and the cause of their beautiful colour is still somewhat of a mystery.
Generally, the cause of the purple in diamonds is thought to be due to post-growth plastic deformation in the earth; however, the exact nature of the defects responsible for the purple colour is still uncertain. A distinctive feature of natural purple diamonds is the presence of parallel deformation lamellae or graining with concentrated colour. Therefore, the purple colouration may vary in strength depending on the viewing angle of the stone.
The majority of purple diamonds were found in the Argyle mine in Western Australia; however, in recent years, one of the reoccurring sources of purple diamonds was the Siberian region of eastern Russia. Purple diamonds are occasionally found in all the Siberian deposits, but they are often recovered from the pipes of the Mir kimberlite field. However, it is worth mentioning that the majority of diamonds from the Siberian deposits are pale. A more recent source of fancy purple diamonds is Quebec, Canada.
Evaluating the Colour of Purple Diamonds
The colour evaluation of purple diamonds has three main components: hue, saturation and tone.
Hue is the visible colour of a diamond, and the primary hue of purple diamonds is purple. However, fancy purple diamonds usually have various secondary hue modifiers such as pink, grey or brown, which explains the absolute rarity of pure purple specimens and their extremely high market value.
As a rule, secondary hues that enhance the primary hue or do not detract from it add value, whereas secondary hues that detract from the primary one diminish the price. Purple diamonds with pink secondary hue command higher prices than purple diamonds with grey and brown modifiers.
Often, purple acts as a modifying hue to other fancy colour diamonds. For example, it adds a beautiful shade to pink diamonds, raising their value because of the added colour richness.
Saturation refers to the intensity of the colour. Purple diamonds are classified using the following colour intensity grades: Light, Fancy Light, Fancy, Fancy Intense, Fancy Vivid, Fancy Deep and Fancy Dark.
As a general rule, the more saturated the colour of a diamond, the more valuable it is. That is why diamonds that have vivid purple colour are much more desired and expensive than those with light colour.
Tone refers to how light or dark the colour is. The choice of tone depends on your personal preference; however, a stone with a darker tone may appear more intense in colour.
Evaluating the Clarity of Purple Diamonds
The clarity of purple diamonds is graded the same way as that of colourless stones. The fewer inclusions, the higher the clarity grade. High-clarity purple diamonds are more valuable, but this characteristic is not crucial for fancy colour diamonds. The purple colour tends to hide imperfections, so the appearance of purple diamonds is less affected by flaws compared to colourless diamonds.
When choosing the clarity of purple diamonds, look for a stone that is eye clean, meaning the diamond with no visible inclusions is more desired. Purple diamonds in the SI1 – SI2 clarity range may look stunning and do not differ significantly from diamonds in VS or even the VVS range.
Evaluating the Cut of Purple Diamonds
The cut quality of purple diamonds, and all fancy colour diamonds in general, is not graded the same way as it is for colourless stones. Unlike colourless diamonds, fancy diamonds are not cut to maximize fire, brilliance and scintillation, these characteristics are considered secondary.
Purple diamonds are cut to maximize colour intensity, usually into fancy shapes. In other words, the proportions considered ideal for colourless diamonds will not always be the best to bring out the colour of purple diamonds. Keep in mind that an excellent cut purple diamond costs a premium, so when choosing one, it is better to focus on the stone’s hue, saturation, tone and even colour distribution and not judge the diamond using traditional cut grades.
Purple Diamond Rarity and Value
Natural purple diamonds are one of the rarest colours in the fancy colour diamond family and are arguably second only to red diamonds in rarity and value.
The most valuable of all purple diamonds are those that feature an even purple colour throughout the gem and do not have any secondary hues. However, since purples compete with red diamonds in rarity and value, any purple diamond modified by red is highly sought-after and on par with pure purple diamonds in terms of price per carat.
Regardless of their cut quality and size, natural fancy purple diamonds are highly sought-after and appreciated by collectors.
Featured image diamonds: Dmitrii Stoliarevich / Dreamstime. A derivative work by Diamond Buzz