Ametrine is a natural occurrence that greatly fascinates me. It's a beautiful mineral combining the mystical colors of Amethyst and the sunset shades of Citrine, two types of quartz.
Unique combinations of quartz are not rare. The concept of 'phantom quartz' is also very interesting and easily noticeable in many samples (this specifically is a topic for another post.)
However, there's speculation that the ametrine as a mixture of amethyst and citrine might not actually exist.
Ametrine Itself
Ametrine is also referred to as Bolivianite, named after its first discovery location, Bolivia. It is solely found in the Anahi mine in the southeastern Bolivia region. It is speculated that it was found and partially mined in the 1600s, then rediscovered more officially in 1960 then began to be extracted in the late 1970s.
As said, its a combination of two quartz types: amethyst and citrine. For its unreal appearance, it became popular in the jewelry and spiritual niches. As for the geologic field, it is a somewhat disagreed on sample. Some sources speculate that Ametrine is not an actual combination of the two stones.
To explore that hypothesis, let's go through the properties of the quartz's themselves. Starting with...
Amethyst
Amethyst is a very iconic quartz consisting of shades of purple. Alongside the base chemical compound of SiO2, it contains impurities of Iron in a +3 oxidation state, Fe3+.
Specifically, the iron is included in the mineral's color center. A color center is the result of a forming mineral undergoing extreme heat. Some of its electrons are shaken up so much that they leave the structure. This leaves a hole for possible surrounding electrons and atoms that could make the mineral stable again.
At some points in the amethyst structure, iron will replace silicon, specifically Fe3+ replacing Si4+. This leaves another extra space, so either hydrogen (H+) or sodium (Na+) can also enter the structure, since both of these have a single oxidation level.
It doesn't take too many of these replacements for the deep amethyst purples to occur, so iron is not listed in the mineral's chemical formula. If it was, amethyst may not be considered a quartz because of a differing formula.
Naturally, amethyst occurs in purple. However, it can also be transformed to appear orange or yellow (rarely, green.)
Heat treating is intense artificial heating or radiation of a stone. It's an 'acceptable' type of treatment in the jewelry industry. Treatments are different kinds of processes made to stones that can make them more beautiful and therefore valuable. What is acceptable or not does not particularly interest me, as in my opinion, the field of jewelry is unacceptable itself. Regardless...
Heat treating is a scientific and relevant process to the discussion of ametrine. Heat treating sets out to recreate the heating process that a mineral undergoes when it is forming, but used to explore the minerals further properties. As amethyst forms, it turns from a clear mass of silicon and oxygen to a gradual purple color. In lab heating, the purple color centers of amethyst begin to break down and instead transform the mineral to a sunset orange.
This spectacularly useful (and beautiful) image is from Amir Akhavan, who has an incredibly impressive catalogue of mineralogy related photos. This image specifically showcases the different states of heat treatment that amethyst goes through. The top left is natural amethyst without any treatment. The top right has been under UV light for 3 entire months and the bottom left has been heated at 380 C (716 F, 653.15K) for 8 hours.
The bottom right is the result of 12 hours at 450 degrees C, or 842 F. As you can see, the purple color has been completely replaced by an almost caramel orange. Parts of this orange color can be seen in the bottom left sample as well, though the purple sections are still more dominating.
(Small tangent, there's a small, not even very popular, misconception that Amethyst can occur as green as well. This is just confusion with the other quartz type, Prasiolite. Prasiolite does also have inclusions of iron within it resulting in its color, but these are in a +2 oxidation state, contrary to amethyst's +3. Some certain samples of amethyst will turn green when heat treated which could also be another cause of the confusion.)
To wrap up Part 1...
You can probably see where this discussion is going after revealing amethyst can change color to coincidentally the exact orange shades seen in ametrine. While you did correctly assume my general opinion of the topic, I believe it is an incomplete argument to not touch on the second proposed ingredient of ametrine, citrine.
In Part 2, I'll explore natural citrine, how its own color centers form, the ongoing mystery and disagreements of it, and how it all relates back to ametrine.
Thank you all so much for reading.
Sources:
https://www.mindat.org/min-7606.html
Mindat is a wonderful website that is incredibly expansive on all different aspects of crystals and minerals. I use it as a main source for various mineral information.
https://www.geologyin.com/2015/08/changes-in-color-of-amethyst-by-heat.html
Geology In explored the picture of the heat treated amethyst, providing a great and easily understood explanation of heat treatment.
https://fentonand.co/en-us/blogs/inspiration-and-guides/everything-you-need-to-know-about-heat-treated-gemstones
Though a commercial source rather than scientific, it does briefly talk about treatments of gems as a whole. I used it as a source, so I will list it fairly.
https://www.webexhibits.org/causesofcolor/12.html
I definitely need to explore this website more, but this specific article talks about color centers in a few different samples of minerals: fluorite and smoky quartz.
https://www.gia.edu/ametrine-history-lore
This article talks about the history of the Anahi mine and its beginnings in extraction.
https://www.mindat.org/gallery-11885.html
Amir Akhavan's photo gigantic photo gallery. A wonderful thing to surf through with a very charming introduction.
Rainbow Lattice Sunstone is a beautiful occurrence... that isn't actually a type of sunstone.
When Orthoclase mixes with Hematite and Magnetite, this beautiful pattern is created:
Rainbow Lattice Sunstone, that I will be abbreviating to RLS for my own sake, is a type of Orthoclase Feldspar with specific inclusions of Hematite and Magnetite.
Feldspar is a mineral group that classifies any mineral containing aluminum tectosilicate, plus a cation such as calcium, potassium, or sodium. In the case of orthoclase, it's potassium.
Orthoclase has the chemical formula KAlSi3O8. It is a specific feldspar mineral that makes up most of igneous rocks.
Sunstone is a real mineral and also a type of feldspar, but has a slightly different formula to orthoclase that differentiates the two. The reason RLS is called Sunstone is not because of its chemical properties, but because of its sunray-like appearance.
Orthoclase feldspar makes up the base of RLS. The namesake, rainbow lattice, comes from its two inclusions.
What is an inclusion anyways..?
This is a smaller piece of another mineral, or sometimes organic matter, that is trapped inside a larger sample of a mineral. This picture of RLS is a great visual for that concept.
Hematite is those little orange inclusions that sort of look like bubbles. If you have seen larger hematite samples before, this may surprise you, because it usually looks black, pictured below.
Hematite actually has a red-orange streak, meaning when scratched on a metal or porcelain plate, it leaves behind that orange color residue. It forms in hexagonal shapes, so those little inclusions are actually very messy six-sided face.
On the other hand, Magnetite is the perfect, black triangles. Magnetite is a great mineral that deserves its own entry, but it often forms in these triangular shapes that don't even look real.
These two inclusions together form a lattice that, at certain angles, results in the iridescent rainbow patterns. It's truly a magnificent sight!!
Ethically...
RLS is found in Australia, in Eastern Arrernte, which is Aboriginal land. Asterism Gems is the company that mines and sells these minerals claim they work in harmony with the Easter Arrernte people and are determined to learning about and respecting their culture. As far as I can research, Asterism Gems is the only company using RLS commercially.
RLS is the banner for this blog. It was one of the first mineral samples that I researched in full and really fell in love with it. It has such amazing properties and I especially love the close up image of its inclusions.
