Is autunite dangerous
Autunite is 49% uranium by mass and it crumbles on its own. Dehydration to meta-autunite costs it 18% of its volume, and that flaking is the actual hazard.
Autunite is radioactive and is 49.2% uranium by mass, calculated from its formula Ca(UO2)2(PO4)2(H2O)11. The practical hazard in a collection is not the radiation from an intact crystal but dust and radon, because autunite dehydrates irreversibly to meta-autunite at room temperature, loses about 18% of its volume doing so, and flakes apart. It is a uranyl phosphate, it fluoresces strongly, and a flaking specimen is the problem. This is not health or legal advice.
In short
- Autunite is 49.2% uranium by mass by stoichiometry from its formula, and meta-autunite — what it turns into on your shelf — is 54.2%. For comparison, uraninite is 88.2%. Autunite is a major uranium mineral, not a trace-bearing one.
- The Handbook of Mineralogy's physical properties line says four words that matter: “Dehydrates in air. Radioactive.” Both are ordinary statements of fact about the species and both have consequences for storage.
- It disintegrates by itself, and the arithmetic says why. Losing five of eleven waters costs 9.3% of the mass while density rises about 10%, so the crystal ends up occupying roughly 18% less volume. Tabular crystals crack and flake.
- That flaking is the hazard, not the intact crystal. A uranium mineral you cannot inhale is a very different proposition from one shedding fine particles into a drawer, and autunite is the species most likely to do the second.
- Hardness 2 to 2.5 with perfect basal cleavage means it is soft enough to powder under handling that would not mark most species. Do not clean it, brush it, or carry it loose.
| Species | Formula | Uranium by mass | Hardness | Stability on a shelf |
|---|---|---|---|---|
| Autunite | Ca(UO2)2(PO4)2(H2O)11 | 49.2% | 2 to 2.5 | Dehydrates irreversibly in air |
| Meta-autunite | Ca(UO2)2(PO4)2·6H2O | 54.2% | 2 to 2.5 | The stable end of that process |
| Torbernite | Cu(UO2)2(PO4)2(H2O)4·8H2O | 47.1% | 2 to 2.5 | Dehydrates to metatorbernite |
| Uraninite | UO2 | 88.2% | 5 to 6 | Stable, but oxidises at the surface |
The honest answer, and where it stops being ours to give
This page is not health advice, radiation-protection advice or legal advice, and we are not qualified to give any of the three. What follows is mineralogy and arithmetic, which is what a mineral site can properly contribute.
Autunite is radioactive. The Handbook of Mineralogy states it flatly in the physical-properties line, alongside Dehydrates in air and Strong yellow-green fluorescence in UV. It is a uranyl phosphate and uranium is most of what it is made of.
The questions we deliberately do not answer here are: how much is safe to own, what dose a given specimen delivers, whether you need a permit, and how to dispose of one. Those depend on quantity, activity, where you live and what you do with it, and getting them wrong matters. In England and Wales the governing instrument is Schedule 23 of the Environmental Permitting Regulations 2016, published at legislation.gov.uk, which sets out what counts as a radioactive substances activity. If your question is about quantity, exposure, permitting or disposal, take it to the Environment Agency or to a Radiation Protection Adviser, not to a mineral dealer's website.
What we can do usefully is the part that is specific to this species and is not in the regulations: autunite behaves differently from other uranium minerals in a collection, and the difference is what the rest of this page is about.
How much uranium is actually in it
“A uranium mineral” covers everything from a trace constituent to an ore. Autunite is at the ore end, and the figure is calculable rather than a matter of opinion.
Method. Autunite is Ca(UO2)2(PO4)2(H2O)11. Summing standard atomic weights gives a formula mass of 968.24, of which two uranium atoms contribute 476.06. That is 49.2% uranium by mass. This is straight stoichiometry from the formula on the IMA-CNMNC master list, not a measurement of any particular specimen, and a real specimen carries matrix and impurities that lower it.
The same calculation across the group: meta-autunite 54.2%, torbernite 47.1%, uraninite 88.2%.
Note which direction the first two run. Meta-autunite is the more uranium-rich of the pair, because what it lost was water and the uranium stayed. A specimen that has dehydrated on your shelf has not become less radioactive; gram for gram it has become slightly more so, while also becoming more friable. Those two changes are the same event.
Our note on working out whether a mineral is radioactive covers identifying the group from a label, which is the first step and answers most cases.
Why my autunite is falling apart, and why that is the actual risk
This is the part that is specific to autunite and is usually missed.
Autunite converts to meta-autunite at room temperature, irreversibly. The Handbook's meta-autunite sheet puts it as plainly as possible: Dehydrates irreversibly from autunite under ambient conditions, and all autunite localities probably contain meta-autunite. It is not a question of whether your specimen does this. It is a question of how far along it is.
The volume arithmetic explains the flaking. Five of the eleven waters leave, which is 9.3% of the formula mass. The measured density rises from 3.05–3.2 to 3.35–3.55, about 10%. A body that loses 9% of its mass while gaining 10% in density occupies roughly 18% less space than it did. Autunite's crystals are thin tabular plates with perfect {001} cleavage, sitting on a matrix that is not shrinking with them — so they craze, lift and flake.
That is the hazard, stated properly. An intact crystal in a closed case is a contained source. A crystal disintegrating into fine yellow flakes in a drawer is a source of inhalable particles of a material that is half uranium by mass, and it is also releasing radon into the volume it sits in. Our note on storing radioactive specimens sets out the rule that follows — seal for dust, ventilate for radon — and why those two requirements pull against each other.
The process also makes autunite a textbook case of something else: it is a mineral turning into a pseudomorph of itself, and it is the only example the Handbook documents across the 109 species sheets we read.
Handling rules that follow from the mineralogy
Everything here follows from two facts already established: it is soft and friable, and it is half uranium. None of it is exotic.
Do not clean it. Not with water, not with a brush, not ultrasonically. At hardness 2 to 2.5 with perfect basal cleavage, brushing removes crystal rather than dirt, and every method makes particles. Our note on cleaning specimens lists the species that should not be cleaned at all; this is one.
Do not streak, saw, trim or prepare it. The streak test makes powder on purpose, which is exactly wrong here — and autunite's streak is pale yellow, which tells you nothing you did not already know from its colour.
Keep it in a sealed rigid container, on its own, and handle the container rather than the specimen. Loose in a drawer it sheds flakes onto everything around it, and then the contamination is a cabinet problem rather than a specimen problem.
Do not keep it in a bedroom or a small unventilated room, which is the radon side rather than the dust side.
Wash your hands, and do not eat, drink or smoke while handling it. The general rule from our note on toxic minerals in a collection covers it, and ingestion is the pathway that matters most for a uranyl phosphate.
One genuine pleasure, with a caveat. Autunite's strong yellow-green fluorescence is among the most spectacular responses in mineralogy, and looking at it under a lamp costs nothing and creates no dust. Our note on the best UV lamp for mineral collecting covers the equipment; autunite is one of the nine species in our survey whose Handbook sheet names no ultraviolet band at all, so either band is worth trying.
We hold no catalogue and nothing on this site is offered for sale. Our wanted list sets out what we look for, and we do not seek radioactive material. Our collecting notes cover the rest of the hazardous group and how to store it.