Purple Diamonds: What Causes the Colour, Grades, Rarity and Settings

What are purple diamonds?

Purple diamonds are fancy colour diamonds. That means their colour is strong enough to be graded on a separate scale from the D-to-Z scale used for white diamonds. On a grading report, a purple diamond is one where purple is the dominant hue, which is always the last word in the colour name. A stone described as 'Fancy Intense Pinkish Purple' is a purple diamond with a pink modifier. One described as 'Fancy Purplish Pink' is a pink diamond with a purple modifier. That word order changes both the look and the price. To see how purple fits among the other colours, start with our complete guide to fancy colour diamonds.

Pure purple, with no modifier at all, is one of the rarest results in coloured diamonds. Most natural purples carry some pink, grey or brown, and most are small, often under half a carat. Physically they are the same as any other diamond: 10 on the Mohs hardness scale, a refractive index (how strongly the stone bends light) of about 2.42, and tough enough for everyday wear in a sensible setting. Any term here that is new to you is explained in our plain-English jewellery glossary.

What causes the colour in purple diamonds?

Most diamond colours come from a trace element. Nitrogen makes yellow and boron makes blue. Purple is different. In most natural purple diamonds the colour comes from plastic deformation: intense pressure deep in the earth bent and slipped the crystal lattice (the regular grid of carbon atoms) along internal planes. That creates defects which absorb light in the yellow-green part of the spectrum, centred around 550 nanometres. Take yellow-green out of white light and what reaches your eye is pink to purple.

This is the same mechanism behind pink diamonds, purple's closest relative, and the rare red diamonds at the far end of the same spectrum. The differences are in how strong the absorption is and exactly where it sits. Because the colour forms along slip planes, natural purples often show colour graining: thin parallel bands of colour you can see under a loupe (a 10× hand magnifier). Graining is a useful clue that the colour is natural, though it is not proof on its own.

A second group, the violet and greyish violet diamonds, is linked to hydrogen in the crystal alongside nitrogen-related defects. These came mainly from Argyle in Western Australia and tend to look cooler and bluer. Lab-grown and treated purples are coloured by yet another defect, the nitrogen-vacancy (NV) centre, covered further down. For contrast, natural radiation in the earth is what produces green diamonds, coloured by natural radiation, a completely different process again.

What is the difference between purple and violet diamonds?

GIA treats purple and violet as two separate hues. Purple sits between pink and violet on the colour wheel and leans towards red. Violet sits between purple and blue and leans towards blue. In daylight, a purple diamond looks like orchid or grape; a violet diamond looks closer to lavender or a blue-grey.

Violet diamonds are very often greyish, so the grey modifier is common. If you like that muted, smoky look, our page on grey diamonds and the greyish modifier shows how grey changes a colour. A greyish violet is not a lesser stone. It is a distinct look, and Argyle violets have been among the most keenly collected coloured diamonds of the past two decades.

How are purple diamonds graded for intensity?

A lab grades a coloured diamond face-up, under controlled daylight-equivalent lighting, by comparing it with reference colours. It assesses three things: hue (purple, pinkish purple and so on), tone (how light or dark) and saturation (how strong). These combine into a single intensity grade. Our page on how a lab grades a coloured diamond goes through the process step by step.

The modifier matters as much as the intensity. Pinkish purple and purplish pink are the most common natural results. A greyish or brownish modifier usually lowers the price, sometimes considerably, because the colour looks less pure. Brown in particular can make purple look muddy; buyers of brown, champagne and cognac diamonds want brown as the main colour, while purple buyers generally avoid it. For the rules on word order, see how modifiers and overtones change a colour name, and for every step on the scale, the full Faint-to-Vivid intensity scale.

Clarity and cut work differently in coloured diamonds. Cutters often choose shapes such as cushion, radiant and pear, which hold colour well, and they will accept lower clarity (SI or even I grades) to keep more colour in the stone. The price is driven mainly by hue, intensity, modifier and carat, with clarity a long way behind.

Where do natural purple diamonds come from? The Argyle story

Natural purple diamonds have come from Russia (Siberia), Brazil and parts of Africa, but Australia has a special place in the story. The Argyle mine in the East Kimberley of Western Australia began production in the 1980s and closed in November 2020. Most of its output was brown diamond, but it also produced, very rarely, the pinks, reds, purples and violets it became famous for. Argyle is widely credited with supplying most of the world's pink diamonds over its life.

Argyle's finest coloured stones were sold each year through an invitation-only tender. Purples and violets appeared only occasionally, and almost always under one carat. The best known is the Argyle Violet, an oval of 2.83 carats graded Fancy Deep Greyish Bluish Violet, cut from rough of about 9.17 carats and offered in 2016. A stone of that size and colour is exceptional; a typical Argyle purple weighs a small fraction of that.

Outside Australia, the largest known Fancy Vivid Purple is the Royal Purple Heart, a heart shape of about 7.34 carats, reported to come from Russia. Stones like these show the ceiling of the category; almost everything on the market is far smaller.

Since the closure, no new Argyle diamonds are being mined, so existing stones move through the secondary market. A genuine Argyle stone normally comes with Argyle documentation and a laser inscription on the girdle (the thin outer edge of the stone). Ask for both, and check that an independent grading report agrees with them.

Natural, lab-grown or treated purple diamonds: how can you tell?

There are three kinds of purple diamond on the market, and they cannot be told apart by eye.

• Natural colour: a mined diamond whose purple formed in the earth. Rarest by a very wide margin.
• Treated natural: a mined diamond whose colour was created or changed after mining, usually by HPHT (high pressure, high temperature) processing followed by irradiation and annealing (controlled heating) to form NV centres. Occasionally a thin surface coating is used, which can wear or be damaged by polishing and heat.
• Lab-grown: a laboratory-grown diamond, made by CVD (chemical vapour deposition) or HPHT growth. Most lab-grown purples leave the growth chamber near-colourless or brownish and are then treated to purple. They are real diamond, with the same hardness and refractive index as natural.

Labs separate them with spectroscopy and UV testing; NV-centre colour, for example, often glows orange-red under ultraviolet light and shows characteristic absorption lines. Our guide to HPHT and irradiation treatments explained covers each process and its durability. What it means for you is simple: the grading report is essential, and the line called colour origin is the most important thing on it.

GIA offers a full coloured diamond grading report (colour grade, clarity, measurements and colour origin) and a shorter identification and origin report, which confirms whether the colour is natural and describes it without a full grade. Lab-grown diamonds graded by GIA or IGI carry reports that clearly state they are laboratory-grown, and the girdle is usually laser-inscribed to match.

How much do purple diamonds cost in Australia?

Natural purple diamonds are priced like the rarest coloured diamonds: per carat, on a steep curve that climbs quickly with intensity and size. Treated and lab-grown purples are a different market entirely, priced at a small fraction of natural colour.

These are broad ranges only. Natural purples trade so rarely that each stone is priced on its own merits, and the modifier makes a large difference: a strong pinkish purple costs far more than a brownish purple of the same intensity. On rarity, natural purple sits near pink and red, far above yellow and canary diamonds, while pure orange diamonds are another rare colour priced on a similarly steep curve. At the other end, most opaque black diamonds sold today are treated and cost very little per carat.

If you want a strong purple at a modest budget, lab-grown is the realistic route, and it is still real diamond. If natural colour matters to you, expect a small stone, often 0.10–0.30 carat, set where it can be seen up close.

Purple diamond vs purple sapphire vs amethyst: which suits you?

Diamond's high refractive index gives purple diamonds strong sparkle, and that sparkle lightens the colour a little; a purple sapphire of similar tone often looks deeper and more saturated, with less fire. If you want a rich purple in a larger size, our page on purple sapphires as a durable alternative compares origins, treatments and lab-created options. Amethyst gives the biggest purple for the money but is softer at 7 on the Mohs scale, so it suits pendants and earrings better than a daily-wear ring.

What are the best settings and metals for a purple diamond?

Metal colour reflects up through a diamond, so the right metal can strengthen purple and the wrong one can flatten it.

• Rose gold: warms and strengthens pinkish purple. A common choice is rose gold claws on a platinum or white gold ring, so the claws match the stone while the band stays white.
• White gold or platinum: keeps violet and bluish purple cool and crisp, and suits greyish violets.
• Yellow gold: yellow is the opposite of purple on the colour wheel, so reflected yellow can make a light purple look greyish or brownish. It works better with deep, saturated stones.
• Halo: a ring of small white diamonds frames a small purple and adds sparkle; contrast can make the centre colour look stronger.
• Bezel or half-bezel: a thin metal rim that protects small stones and suits fragile corners on pears and hearts.
• Three-stone: a purple centre between white diamonds, or between natural or lab-grown pinks, is a classic three-stone layout.

For side-by-side examples across every coloured diamond, see settings and metals that suit coloured diamonds.

How do you choose a purple diamond? Step by step

1. Decide on the hue. Purple dominant, purplish pink or violet: look at examples of each, as they read very differently.
2. Read the colour origin first. Natural, treated or laboratory-grown changes the price more than anything else on the report.
3. Check intensity and modifier. Fancy Intense and above for strong colour; be cautious with brownish modifiers if you want a clean purple.
4. View it in more than one light. Daylight and warm indoor light, in photos or in person.
5. Look for treatment clues. Ask about coatings and NV-centre treatment, and read up on signs a coloured diamond has been treated before you compare stones.
6. Compare millimetres, not just carats. Small natural purples vary widely in face-up size for their weight.
7. Plan the metal and setting. Choose rose, white or yellow metal to suit the hue, and protect any points or thin corners.