Ultra-Pure Quantum Crystals from an Abandoned Mine in the Atacama Desert

17 min readJan 8, 2026--A Two Part Post on the Immense Promise and Ecological Tragedy of Natural Herbertsmithite CrystalsIntroductionHello Everyone, My name is Dr. Aaron Breidenbach. For those who haven’t been following my journey, I grew crystals of Zn-Barlowite and Herbertsmithite in my PhD at Stanford. These crystals are candidates to be a new novel state of matter called a “quantum spin liquid” (QSL). I just published a paper in nature physics (free version here) with Young Lee’s Lab, providing the strongest evidence to date for the presence of this mythical magnetic state in these crystals. Due to these properties, Zn-Barlowite and its sister QSL candidate material Herbertsmithite have immense potential to be used in future large scale quantum computers. Given what LLMs are currently doing on silicon, one can only imagine how society-altering these crystals might be one day if we can actually fashion them productively in a quantum computer.What’s more amazing to me about these crystals is that they grow in nature as well. I will emphasize that this is an absolute anomaly. To the best of my knowledge, this is the only crystal with any bulk quantum properties that grows in nature (other than its sister materials like Atacamite). Quantum physics is hard, and me and all of my colleagues in condensed matter physics spend hours intentionally mixing very specific ratios of strange elements to make synthetic quantum crystals like superconductors. This is the norm. And yet, somehow, these crystals, among the most mysterious of them all, just grow naturally, and they have probably been sitting around in the earth’s crust for millions of years or more, long before the dawn of apes as a species.With this mystical mystery as motivation, I recently set off on an adventure to the Atacama Desert in Chile to find these crystals in their natural habitat. What I found astounded me for many reasons. This is a two part post. In the first post here, I will focus on the immense potential that natural crystals have for advancing our knowledge of quantum physics.

Then, in the second post, I will focus on how these crystals are tragically being destroyed in large scale ecologically damaging mining practices in the Atacama Desert.(For other content related to this project, including interviews, videos, and published papers, please see my website, thequantumarcheologist.org)The Discovery and the PromisePress enter or click to view image in full sizeA photo of all of the Herbertsmithite crystals I found in a single boulder in an abandoned mine in the Atacama Desert. While I have yet to separate these crystals, I estimate that I have at least twice the mass of Herbertsmithite crystals from this one discovery as compared to what I grew in 6 years as a graduate student at Stanford.Press enter or click to view image in full sizeA close-up image on one of the higher-quality Herbertsmithite crystal formationsIn my journey to Chile I was successful in finding the legendary natural Herbertsmithite crystals. I made this discovery in collaboration with Anthropologist Vicente Carrasola Vega from the University of Chile. He is the one that spotted the crystals in the field, and he proved to be an indispensable guide, translator, and knowledge holder in the desert. Amazingly, we found these crystals in the waste tailings of the abandoned San Francisco mine. We then verified the identity of these crystals with x-ray scattering with the help of Professor Joseline Tapia and staff in the geology department at the Universidad Católica del Norte in Antofagasta Chile.Press enter or click to view image in full sizePowdered X-ray spectra of the crystals I found, confirming its identity as Herbertsmithite mixed with AtacamiteThis was no small discovery either. We found a lot of these crystals. I have yet to separate and measure all of these crystals, but I’m conservatively estimating by eye that we have at least 10 grams of hexagonal green crystals (but probably much more). I’m hoping most of this is Herbertsmithite, and we also have at least a few grams of the related minerals Atacamite and Zn-Paratacamite. (The x-ray scattering suggests these crystals are mostly Herbertsmithite, ~65% by composition, but this is unreliable and limited to one sample.

Future measurements will be more accurate in pinning down an exact ratio and amount).For comparison, the lab grown crystals are very difficult to grow. It takes about a full work week of preparation and 9 full months of waiting for them to grow to full size. This process also involves a lot of training to master. It is additionally very expensive in terms of equipment overhead (>$10,000) and the reactant chemicals required (~$100 per growth attempt). This synthetic process only produces about 1–2 grams of crystals per test tube and is only successful about 45% of the time. It seems that Vicente and I found nearly 10 times this amount in this single discovery. Meanwhile, the only equipment overhead was a pair of humble $15 pickaxes we picked up at the local mining outlet in Calama.Press enter or click to view image in full sizeThe waste pile outside of the San Francisco mine, near Sierra Gorda Chile. This is the location of my discovery of natural HerbertsmithiteThis is reason enough to study the natural crystals. However, I also found something that is truly spectacular in my geological studies. Natural crystals of Herbertsmithite have been measured to be more pure than our laboratory synthetics. This measurement was done via electron microprobe microscopy by the late Michael Scott in the geology department at the University of Arizona. This measurement was performed on samples of Herbertsmithite from the San Francisco mine outside of Sierra Gorda, Chile; this is the exact same mine where we found our crystals. (P.S. Michael Scott himself is also a legendary mineral collector, who helped create the very University of Arizona RRUFF mineralogical database that I linked to above).This is, quite frankly, incredible, and has huge implications for quantum physics. Magnetic impurities are the cause of a lot of debate and uncertainty in QSL research . The crux of the purity issue is in the copper to zinc ratio. In the ideal chemical formula, this ratio is 3:1. In our best laboratory synthetics, we have only achieved a ratio of 3.15:0.85; there’s always a certain amount of excess copper. The natural crystals, on the other hand, are far closer to the ideal ratio at 2.98:1.02, and actually contain a slight excess of zinc.

At first, this difference in purity might seem quite small, but the implications in this system are huge. In the ideal material, these crystals host two dimensional Kagome layers which contain the magnetic Cu²⁺ ions. Each layer is separated by a non-magnetic Zinc spacer layer. This means that the magnetic physics is effectively two dimensional, which is why these crystals can host such an exotic quantum state of matter.Press enter or click to view image in full sizeBall and stick model of Herbertsmithite in an out of plane view. The kagome layers contain exotic quantum physics if the interlayer maintains magnetic separation. However, interlayer sites can sometimes be occupied by magnetic impurity ions. If this happens too frequently, this can destroy the quantum magnetism.The problem is that the excess copper substitutes onto the otherwise non-magnetic zinc spacer layer, which breaks the two dimensional magnetism to some extent, allowing the 2-D layers to “talk” to each other magnetically. Many physicists even think that the presence of these magnetic impurities is enough to destroy the QSL state on the Kagome lattice and/or obfuscate its magnetic signatures. This is where our neutron scattering measurements come in; we found strong evidence that was able to separate out magnetic impurity contributions from Kagome contributions in a convincing way in Zn-Barlowite. Furthermore, we also did this analysis for Herbertsmithite, another likely QSL material with a different impurity environment. The two were nearly identical in their QSL behavior and all differences were well modeled to be due to their different impurity environments (see the nature paper for further discussion).We then went further to provide evidence that the quantum spin liquid state is intrinsically “gapped”. This is a bit of technical jargon, but in practice, this means that the QSL state is robust to perturbations. This is because there is a minimum amount of energy required to excite the state. Therefore, it should not be so fragile that it will fail to a few magnetic impurities lingering around it. This also has large implications that future quantum computers made out of these crystals and their exotic excitations might be far more fault tolerant than other options. Here’s a diagram below that illustrates this:Press enter or click to view image in full sizeFits from our recent nature paper that attempt to separate magnetic impurity contributions from intrinsic quantum magnetism in the two dimensional kagome layer of Zn-Barlowite.

Note that even with high-quality samples with about 20% of potential impurity sites being occupied, the impurity signal is still massive relative to the proposed quantum magnetic signal, at about 5x the size.As amazing and groundbreaking as this paper is, reasonable doubts remain. While the theory we presented is compelling and self-consistent, our models are still far from the only theory that can explain the data that we took. This is especially as the proposed impurity contributions are huge, roughly 5 times larger than the signal coming from the proposed “intrinsic” quantum magnetism in the QSL state.One thing that would provide much stronger evidence for a gapped quantum spin liquid state is a 100% pure specimen of Herbertsmithite with no interlayer impurities. This would make our neutron scattering data far less ambiguous to interpret; in such a specimen, the theoretical “spin gap” would be incredibly clear, and we wouldn’t have to rely on extrapolation from empirical models nearly as much (if at all).Press enter or click to view image in full sizeThe same plot as above, but with the modeled impurity contributions subtracted out. In theory, samples with no-interlayer impurities should look something like this in direct measurements, with there being essentially no scattering at low energies. This is what is meant by the “energy gap”. Measurements strongly suggest that natural crystals have no-interlayer impurities, and I hope to measure this type of scattering signature in them some day.This is what potentially makes the natural crystals so special. They’re not just pure, they’re 102% pure 😊!! Having an excess of zinc instead of an excess of copper means that there should be essentially no copper on the interlayer, and that many of the advantages outlined above should be maintained. The extra zinc relative to the ideal chemical formula would have to go on the Kagome layer, which could theoretically cause problems of its own. However, this could be modeled. And if the ground state is indeed a gapped quantum spin liquid, then it should be robust to this minor perturbation. But the perturbation would be very different in nature. This would make all the difference and make our conclusions far less unambiguous.With this, I will say that this statement does not come without controversy. My thesis advisor, Professor Young Lee, has previously published a paper that argues that it is impossible for zinc impurities to occupy the Kagome layer in these materials.