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Mineralogical ClassificationDiscovery of the first natural hydride

12th Apr 2019 13:28 UTCMarco E. Ciriotti Manager


▪ Bindi, L., Cámara, F., Griffin, W.L., Huang, J.-X., Gain, S.E.M., Toledo, V., O’Reilly, S. (2019): Discovery of the first natural hydride. American Mineralogist, 104, 611–614.


Although hydrogen is the most abundant element in the solar system, the mechanisms of exchange of this element between the deep interior and surface of Earth are still uncertain. Hydrogen has profound effects on properties and processes on microscopic-to-global scales. Here we report the discovery of the first hydride (VH2) ever reported in nature. This phase has been found in the ejecta of Cretaceous pyroclastic volcanoes on Mt Carmel, N. Israel, which include abundant xenoliths containing highly reduced mineral assemblages. These xenoliths were sampled by their host magmas at different stages of their evolution but are not genetically related to them. The xenoliths are interpreted as the products of extended interaction between originally mafic magmas and CH4+H2 fluids, derived from a deeper, metal-saturated mantle. The last stages of melt evolution are recorded by coarse-grained aggregates of hibonite (CaAl12O19) + grossite (CaAl4O7) + V-rich spinels ± spheroidal to dendritic inclusions of metallic vanadium (V0), apparently trapped as immiscible metallic melts. The presence of V0 implies low oxygen fugacities and suggests crystallization of the aggregates in a hydrogen-rich atmosphere. The presence of such reducing conditions in the upper mantle has major implications for the transport of carbon, hydrogen and other volatile species from the deep mantle to the surface.

12th Apr 2019 13:55 UTCJolyon Ralph Founder


12th Apr 2019 14:39 UTCPaul Brandes Manager

Cool indeed, especially the last couple sentences.....

12th Apr 2019 20:33 UTCFrank K. Mazdab Manager

This an interesting occurrence! I look forward to reading this paper and the related ones on the locality.

It also brings to mind that we have a mineralogically identical occurrence in Argentina that maybe needs "re-visiting":


The mineralogy here is remarkably similar... hibonite + grossite + V-rich aluminous spinels + spheroidal and dendritic inclusion of metallic V.

"Re-visiting" both because it would be cool to literally visit, but also because it seemed the consensus thinking on the Argentinian locality was leaning towards it being a smelter product (and there's even a note to that effect in the locality description). Prior to the description of the Mt. Carmel occurrence, I'd even wondered if the Argentinian rocks had been created in someone's lab (my guess had been thermite reaction), and indeed the Argentinian samples aren't scattered tiny inclusions in xenoliths but appear to be hand-sample-sized rock fragments. Still, with two places in the world now with this odd assemblage, it makes one go hmmm.

12th Apr 2019 22:46 UTCRalph Bottrill Manager

The Argentinian occurrence look very dodgy, collected by a mineral dealer with no site description and the rock type is incompatible with the geology of the district. But the Mt Carmel occurrence is well described and sounds valid and quite amazing!

13th Apr 2019 00:06 UTCFrank K. Mazdab Manager

Hi Ralph,

totally agree that the Argentinian occurrence does, well, raise eyebrows, for all the reasons you indicate. But it is compelling that the assemblages and textures from the two places are pretty much identical, really only differing in grain size. And there technically is a reference related the new V-spinel found at the Argentinian locality (albeit in a pay-to-play MDPI journal). Indeed, that's when the locality name changed from "un-named hibonite occurrence" to "dellagiustaite occurrence". I also thought there was originally mention in the reference list to an in-prep paper first-authored by Tony Kampf at NHM in LA, but maybe I'm mistaken about that or the effort was quietly dropped. In any case, that original "reference" certainly isn't in the reference list anymore.

13th Apr 2019 09:13 UTCAlfredo Petrov Manager

A few of the Argentine pieces appear to have ovoid depressions on the surface that look a bit like slag bubbles, and none of the pieces seem to have any kind of matrix rock attached. Not proof of anything, but it did make me suspicious. (Like the diaoyudaoite from New Jersey - no matrix, unlikely chemistry, and old chromium refineries nearby, so almost certainly waste byproducts of chromium refining, although some of the local collectors there still desperately want to believe it could be natural.) And the Argentine material resembles the waste from a Norwegian niobium refinery, as was pointed out to us years ago by one of our Scandinavian users.

13th Apr 2019 09:41 UTCRalph Bottrill Manager

I am a bit surprised that the IMA didn't question its occurrence and I'm not sure how well peer-reviewed the Minerals open source publication is?

13th Apr 2019 11:01 UTCAlfredo Petrov Manager

The IMA didn't question diaoyudaoite either, although it seems to be anthropogenic in all of its known localities. The IMA generally trusts authors' proposals as far as origin goes, and judgement is made only on the mineralogical characteristics in the description. Authors are not asked to prove that their material is natural, so there are several dubious species. Trust nothing without a matrix and geological context ;))

13th Apr 2019 21:17 UTCBranko Rieck Expert

I am a little surprised by the title, because we have known nitrogen hydride (ammonia) for a long time from natural sources. What Bindi et al. meant was probably "Discovery of the first natural metal hydride".

I am also surprised that the reviewers let that slip through.

I might however be in error on the nomenclature side, as I am currently on a field trip and do not have my IUPAC Nomenclature of Inorganic Chemistry handy.


13th Apr 2019 21:38 UTCŁukasz Kruszewski Expert

This locality and its assemblage are sometimes questioned, similar to the type locality of dellagiustaite in Argentine. But after reading 1 or 2 papers on the Israeli one, I think it is, indeed, natural.

Regarding NH3 - I agree with Branko: it is now almost certain that NH3 ices are common in the Solar System and we may expect some NH3 minerals, possibly, in the future...

13th Apr 2019 22:08 UTCFrank K. Mazdab Manager

Hi Branko,

although I think IUPAC both "officially" and traditionally consider ammonia to be nitrogen hydride as you note, that convention actually violates the more general consideration that the more electronegative element should be give the suffix (and so by that criteria, ammonia might be reasonably considered as H3N... hydrogen nitride). I suppose since the electronegativities of nitrogen and hydrogen are relatively close and ammonia falls right on that fuzzy boundary, the mineralogy reviewers thought nomenclature flexibility might be in order here... perhaps chemistry reviewers, however, would have been more picky about the word choice. Or alternatively, maybe either the authors or reviewers (or both) recognized IUPAC's inconsistency here, and simply decided to follow the more general rule... you know, standing up against "the man"... lol.

25th Apr 2019 09:10 UTCAndrew G. Christy Manager

Hi Branko,

For ammonia to be a mineral species, naturally-formed, solid, crystalline ammonia would have to have been characterised and proposed. Gases do not count, nor do liquids except mercury.

And as Frank says, using electronegativity as a criterion, ammonia would count as a hydrogen nitride rather than nitrogen hydride. Similarly, methane hydrate (which is a potential new mineral, once someone proposes it) would be a hydrated carbide of hydrogen except it falls into the special "organic" catgeory.

25th Apr 2019 09:16 UTCJolyon Ralph Founder

> For ammonia to be a mineral species, naturally-formed, solid, crystalline ammonia would have to have been characterised and proposed

Yes, but the paper title says "First natural hydride" not "first natural hydride mineral species" - minor point but Branko is absolutely right.

And although the IMA can't approve ammonia as a mineral species, we all know that it exists as a naturally-formed solid crystalline form in many parts of the solar system, and although mineralogists haven't studied this because they don't want to, it has been studied well enough by other scientists that mineralogists probably don't need to bother.

I understand the reasoning why, but it always seems to me rather unscientific to say "this cannot be a mineral because it doesn't exist in the right form in this narrow band of temperature/pressure that I happen to find comfortable to work with in my lab" :)

25th Apr 2019 09:45 UTCDavid Von Bargen Manager

I understand the reasoning why, but it always seems to me rather unscientific to say "this cannot be a mineral because it doesn't exist in the right form in this narrow band of temperature/pressure that I happen to find comfortable to work with in my lab" :)

But the IMA says that this does not matter.

25th Apr 2019 10:05 UTCJolyon Ralph Founder

Good. I think things are changing out of necessity as we do more research outside of the solar system. For well-known and well-characterised materials such as ammonia, carbon dioxide, nitrogen, etc then I see no reason why we can't characterize their physical properties from synthesized material rather than having to dig out a piece off a comet, ship it home and somehow XRD it while frozen.

25th Apr 2019 10:49 UTCDavid Von Bargen Manager

Well, it hasn't gone that far. You still need to deposit the type specimen in a public institution (although it doesn't necessarily have to survive in the collection). You don't need to name a mineral to study the phase and check it's important properties (most of the field of high pressure mineralogy would be wiped out - studies of the core and mantle conditions).

25th Apr 2019 11:34 UTCMarco E. Ciriotti Manager

I agree, Dave.

25th Apr 2019 12:46 UTCFrank Keutsch Expert

What about protonated nitrogen hydride, just a different form of nitrogen hydride, but still nitrogen hydride. That occurs naturally in mineral as far as I know!


25th Apr 2019 14:27 UTCJolyon Ralph Founder

It's true that we don't need to name them to study them, but when we look at questions such as how many minerals are found throughout the earth it's important that we need some way of taking all these other phases into account. Our mineralogy is very crustally biased :)

25th Apr 2019 14:44 UTCDavid Von Bargen Manager

" when we look at questions such as how many minerals are found throughout the earth it's important that we need some way of taking all these other phases into account" You not only have these "theoretical" phases, but also all those partially described species (which are scattered throughout the literature).

25th Apr 2019 16:52 UTCRoger Curry

Echoing Marco, I agree, Dave.

27th Apr 2019 01:05 UTCKyle Bayliff

Actually, according to a recent nature paper I read (Nature vol. 568, pages357–359 (2019)) there was a discovery of an even earlier hydride reported, though this will deviate somewhat from mineralogical discussion. In fact this molecule, HeH+, was reported as the first hydride ever formed in the cooling universe! Obviously, it is a charged ion rather than a neutral crystalline solid, and it is so reactive that it cannot exist outside the vacuum of space, but I think it has VH2 beat!

27th Apr 2019 16:35 UTCBenjamin Oelkers

Maybe just to add a chemist's perspective: Ammonia is a hydride in the broadest sense of the word, i.e., a compound of hydrogen and something else. However, the usual (and IUPAC-recommended) description "ammonia" (or "azane", to be even more systematic) focuses on it being a covalent compound with hydrogen as the electropositive bonding partner. So, in order of usefulness, you could say:

1. nitrogen hydride (almost always a bad idea, does not reflect the actual bonding situation or reactivity)

2. hydrogen nitride (usually also a bad idea, but does reflect the reactivity)

3. azane (absolutely fine, but not very common)

4. ammonia (please, only use this one!)

So, as long as water is not counted as the most abundant hydride on earth, ammonia will also not qualify as a hydride. ;-)

27th Apr 2019 19:27 UTCFrank K. Mazdab Manager

The electronegativity relationship between the constituent atoms in water, despite being akin to that of the constituent atoms in ammonia, is more extreme and so water is uncontroversially hydrogen oxide (or rather more appropriate for covalent materials, dihydrogen oxide). I seem to recall news years ago of some science fair project where a student laid out how this "unfamiliar" compound, dihydrogen oxide, was responsible for so many human deaths but was widely present in the environment and wholly unregulated, to draw attention to, well, I suppose in part, fear-mongering of chemical names and ultimately how scientifically illiterate so much of the population is.

27th Apr 2019 20:59 UTCBenjamin Oelkers

While the difference in electronegativity is undoubtedly more pronounced in water than it is in ammonia, there is still more than enough difference to clearly decide that nitrogen is the electronegative bonding partner. Apart from theoretical calculations and spectroscopic methods, the simplest way to show this is to look at the typical reactions of ammonia in comparison to metal hydrides, e.g. hydrolysis:

δ-δ+ + δ+δ-

NH3 + H2O NH4+ + OH-

δ+δ- + δ+δ-

NaH + H2O Na+ + OH- + H2

The first hydrolysis consists of a simple protonation of ammonia, because the nitrogen atom has a negative partial charge (and gets to combine that with a positive partial charge of the proton from the water molecule). The second hydrolysis is a redox reaction typical of true hydrides: In this case, the negative partial charge lies on the hydrogen atom, which is why it reacts with a proton from the water molecule (no change on that part).

Both reactions occur between a proton from a water molecule (positively charged) and the negatively charged part of ammonia/sodium hydride, thus nicely illustrating the difference in polarisation between the two.

27th Apr 2019 22:32 UTCFrank K. Mazdab Manager

Hi Ben... you'll get no disagreement from me. But "officially", despite your correct electronegativity observation, IUPAC prefers "nitrogen hydride" over "hydrogen nitride" (see the interesting position they opted to place hydrogen in their Figure 1: https://iupac.org/cms/wp-content/uploads/2018/05/Inorganic-Brief-Guide-V1-3.pdf). Still, I suspect they'd rather people just say "ammonia", and then that's one less inconsistency they have to deal with... :-)

27th Apr 2019 22:39 UTCFrank Keutsch Expert

I agree with Ben, that NH3 is not what I think of as a hydride for the reactivity reasons he describes. The official IUPAC name would also include a "tri" for specificity and distinction from other pure NH compounds and there is also the IUPAC name "azane" which usually is only used for substituted forms. I definitely think ammonia is its actual name.


27th Apr 2019 23:11 UTCBenjamin Oelkers

Hello Frank!

Yes, I noticed that too. This whole sequence is quite interesting, to say the least. It appears to be chosen in order to respect the traditional way of writing H2O and NH3, and to provide consistency within the groups of the periodic table rather than to be physically meaningful. However, in the full recommendations (IUPAC Red Book 2005) you will also find "azane" and "ammonia", mentioned in Table IR-6.1 (page 85). To make matters even worse, two systems of producing names are given in this text (substitutive and additive nomenclature, respectively), both of which are said to equally "good".

Apart from all of that, the IUPAC does only matter so much in real life. Even if they proposed to completely abandon the term ammonia, that would most likely be largely ignored by researchers and teachers alike.

27th Apr 2019 23:55 UTCSteve Hardinger Expert

Chemists tend to ignore IUPAC nomenclature, especially when the molecule in question has a history of another name. Example: Methylbenzene (IUPAC) versus toluene (so-called 'trivial name), and ethanoic acid (IUPAC) versus acetic acid (very old name). It gets even worse with pharmaceuticals.

In addition there is no consistent way to write formulas. Some say, "list elements alphabetically", or "by electronegativities", "cation first", or (if you're an organic chemist, like me) carbon first then everything else alphabetically. Of course there are all sorts of in-between bastardizations (no offense, Jon Snow) meant to give some structural information.

Acetic acid might be written as H4C2O2 (by EN), CH3CO2H ('bastardized'; meant to show a methyl group CH3 bonded to a carboxyl group CO2H), or (the **correct**, organic chemists' way) as C2H4O2.

Let me extend Benjamin's observation a bit and say that the more complex the name/formula/structure, the more IUPAC rules are ignored. NH3 will pretty much always be ammonia, but compare 'cholesterol' versus its IUPAC name ((3β)-cholest-5-en-3-ol) versus (even worse) it's 'systematic IUPAC name ('(3S,8S,9S,10R,13R,14S,17R)-10,13-dimethyl-17-[(2R)-6-methylheptan-2-yl]-2,3,4,7,8,9,11,12,14,15,16,17-dodecahydro-1H-cyclopenta[a]phenanthren-3-ol). To organic chemists, cholesterol is merely a moderate-sized molecule.
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