Natural Citrine or Heated Amethyst?
Heating Amethyst to Produce Citrine
People are often surprised to learn that citrine is a relatively rare variety of quartz. The stone is named after the French word 'citron', meaning 'lemon'.
Most citrine sold around the world is produced by heating amethyst. The shade of yellow depends on the original colour of the amethyst, the temperature at which it was heated, and for how long.
In rough heated amethyst, the colour is often a deep, almost burnt shade of orange. White or colourless quartz is often visible towards the base of the crystal, and colour zoning, a typical characteristic of amethyst, is usually still visible after heating.
Natural citrine can also show some colour zoning, but it looks different to how it appears in amethyst. Therefore, that alone does not necessarily mean a stone was originally amethyst.
Citrine ranges from yellow to yellow-orange and yellow-green. Some stones exhibit smoky tones, giving it a golden brown or dark brown appearance.
Citrine can also contain phantoms, which are ghost-like outlines of earlier growth within the crystal.
Identifying natural citrine is not always straightforward. Iron staining can give quartz a yellow colour, suggesting that it may be citrine. The staining comes from iron-bearing minerals coating the surface, filling cracks, or trapped inside the crystal, rather than from iron within the crystal's structure.
Heated amethyst is often easy to identify, but there are exceptions. Polished stones can be more difficult.
The fact that natural citrine is so rare means that large pieces, both rough and polished, are not easy to find. They're also likely to be expensive.
Heating Stones to Alter Colour
Amethyst's purple colour occurs when traces of iron within the quartz are exposed to natural radiation. Exposure to radiation changes how the crystal absorbs light.
Heat has the opposite effect. When amethyst is heated, the colour centres responsible for its colour can be disrupted, causing its colour to fade or disappear. As heating continues, the iron within the quartz changes and produces shades of yellow, orange or brown.
The final colour depends on the stone's characteristics and the heating conditions.
Amethyst from certain locations turns green when heated, which is how prasiolite, often labelled as green amethyst, is produced. Natural prasiolite is very rare.
Heating doesn't remove the iron, as some claim. It changes the iron within the structure of the crystal and how it responds to light.
It's often reported that when amethyst is heated to around 450°C (842°F), it starts turning yellow. In a 2020 study using material from South Africa, the stones began losing their colour at about 380°C. They then went through a pale green stage at 420 to 440°C, which the authors describe as prasiolite.
As the heat rose to above 440°C, the crystals turned yellow. The colour deepened as the temperature increased.
The finest citrine-like colour was obtained at about 560°C. The authors state that the darker the original amethyst, the greater the change.
Heat is often used to enhance or alter the colour of minerals. It can also remove unwanted characteristics, such as wisps of colour.
Although blue topaz occurs naturally, it's extremely rare. Natural blue topaz bears little resemblance to the popular Sky, London, and Swiss Blue gemstones, which are produced by irradiating colourless topaz and then heating it. The same process is used to produce lemon quartz.
Smoky quartz and some other quartz varieties can also be used to produce 'fake' citrine.
Many rubies and sapphires are heated to improve their colour. A fine-quality ruby that has not been heated is rare.
Aquamarine is also commonly heated to turn greener stones into shades of blue.
Real citrine is generally expensive, particularly for premium-grade stones. Therefore, heated amethyst has long been accepted as the next best thing.
Real Citrine: What to Look For
A point worth remembering when buying citrine is that most material is heated amethyst. The problem is that often, the retailer will not have been told by their supplier, or, in some cases, have been led to believe it's natural citrine when it's not.
One of the most obvious clues for distinguishing one from the other is the presence of white or colourless quartz towards the base of the crystal. This is because there's less iron in the lower section. The colour is often much deeper towards the tip. It's believed this is because of the mix of iron in the water as the crystal grows.
Colour is one of the easiest ways to identify 'fake' citrine because it will often have a rich, almost burnt-orange appearance.
With regard to gemstones, it will often be size, price and distinctive changes in colour that would indicate a stone is heated amethyst.
The colour of low-grade natural citrine, which is far more abundant and less expensive, is often very subtle.
Another clue for identifying real citrine is dichroism. Dichroism is a form of pleochroism. Minerals that exhibit this optical phenomenon display different colours when viewed from different directions.
Both amethyst and citrine are weakly pleochroic, but pleochroism disappears once amethyst has been heated.
Testing a stone for dichroism may confirm it's not heated amethyst, but it doesn't guarantee it's natural citrine. This test is not easy to carry out unless you know exactly what to look for.
What's in a Name?
The main issue with producing citrine by heating amethyst is that some people feel cheated.
In the world of rocks, minerals and gemstones, heating and dyeing are relatively common. However, heating a stone to alter its colour is not the same as dyeing.
Dyed agate or chalcedony is relatively common. Most black onyx is dyed agate or chalcedony. Although blue chalcedony occurs naturally, decorative material, including gemstones, is often dyed.
Trade names add to the confusion because they can be misleading about what a stone actually is.
I have often wondered whether it would be more appropriate to call heated amethyst sold as citrine 'yellow quartz', but that presents a whole new set of challenges. Natural citrine is yellow quartz, just as amethyst is purple quartz.
Pink quartz from Patagonia in Argentina is marketed as 'pink amethyst'. The name is contentious because it extends the term amethyst beyond its established purple colour range.
The 2020 study that described pink amethyst, in the Mineralogical Record, used the name in its title and called the stones a new colour variety of quartz. That drew criticism from mineralogists, including the journal's own founding editor, on the grounds that amethyst has meant purple quartz since Theophrastus.
Collectors generally attribute the pink to microscopic inclusions of hematite.
Calling it pink quartz would present another problem. Rose quartz is the pink variety of quartz, and 'pink quartz' is often used to describe a rarer variety that forms distinct crystals.
Although natural citrine geodes have been documented, supporting evidence and photos are difficult to find. If citrine does occur as a geode, it's exceptionally rare. The familiar 'citrine geodes' sold commercially are all heated amethyst.
Prasiolite is a rare green variety of quartz. Much of the material sold commercially is produced by heating 'suitable' amethyst. Only amethyst from a few localities turns green when heated. Most turns yellow.
This material is often marketed as 'green amethyst', which is incorrect.
What is Madeira Quartz?
Madeira quartz is a trade name that has recently been introduced. It clearly takes its name from Madeira citrine.
Madeira citrine is citrine, whether natural or heated amethyst, with a rich orange to reddish-brown, deep saturated colour.
The name comes from the Portuguese fortified wine from Madeira because of the similarity in colour.
Although some people shy away from heated amethyst citrine, it serves a purpose because it lets consumers buy a similar-looking stone at a more affordable price.
When well produced, it can be very nice.
With regard to fine-grade gemstones, the skill and expertise required to cut and polish remain the same whether it's amethyst or citrine.
Is Heated Amethyst Fake Citrine?
The answer depends on how the stone is sold. A fake is any material passed off as something it isn't. In rocks and minerals, that could be a man-made material, such as glass or resin, or may be another natural stone that has been treated to mimic another. Dyed howlite to imitate turquoise is one example of many.
Heated amethyst is a natural stone whose colour has been altered through heat. It hasn't been dyed. If a consumer is aware of what they're buying, and the price reflects the material as heated amethyst, and not citrine, then it should not be considered to be fake. However, if sold as natural citrine, then it's a fake.
That's why terminology matters. The problem is that most retailers call heated amethyst 'citrine' because it's a widely accepted alternative. The term 'heat-treated citrine' is sometimes used but can be misleading because natural citrine can also be heated to enhance its colour.
'Baked' or 'cooked' amethyst is widely used in North America. I prefer 'heated amethyst citrine.'
Article Pictures
The heated amethyst citrine tumbled stones at the top of our article, and the three rough crystals are from our collection.
The retailer holding a handful of "natural untreated rough, fine grade citrine crystals", comes from a listing on a popular online marketplace.
The pink amethyst geodes are courtesy of Bob Harman (FMF Minerals Forum). The photo is clickable and redirects to the original image.
The heated amethyst citrine pendant and natural citrine tumbled stones in our last photo are from our collection.
Pop-up photos
Natural citrine: Courtesy of Rob Lavinsky. Dyed blue agate: Courtesy of James St. John.
The minerals in all other pop-up photos are from our collection.
