Silicon Purity

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How can you be sure? People hear of lots of things that have little or no foundations in reality.....think about many of the things Kramarat claims....he must have heard of those ideas at some point. Come to think of it, despite rolling of eyes and gnashing of teeth, so have we.

Now we have, but without any indication that it actually happens.

And that's really where I am on it. The Open Source app Kalzium that I use has silicon's mass at 28.05...but the highest purity listed for it on their table is 92.some odd and mass of 27.977 with 14 neutrons--and 14 neutrons is also what it says for a mass of 28.05. I was hoping that someone would have heard of a higher purity natural crystal. At 13 neutrons.

I'm seeing yes, but rarely.

Pure Silicon crystals are only occasionally found in nature; they can be found as inclusions with Gold and in volcanic exhalations.

http://www.3rd1000.com/elements/Silicon.htm

Silicon has 3 naturally occurring isotopes Si-28, Si-29, Si-30, with 14,15 & 16 neutrons respectively. Regardless of the number of neutrons in the nucleus, they are all SILICON. There are other isotopes of silicon (all higher atomic weight) that have been made in nuclear reactors but they are too radioactive to be of interest.

Si combines very energetically with O2 and it therefore requires a lot of energy to separate them. It's therefore highly unlikely that any 100% pure Si occurs in nature. I don't see any mention of there being a Si-27 with 13 neutrons.

You may be confusing the atomic weight with % purity.

No, what I had noticed was a discrepancy between what my Kalzium app said about purity at the atomic mass of 28.05.

It's table has a highest listed purity at 92.28%, atomic weight 27.977, and 14 neutrons.

The next heavier isotope has 15 neutrons and a weight of 28.976, but only 4.67%.

I had also already considered the common state we find in nature, SiO3 as problematic, but I figured I'd ask. While Open Source stuff tends to be put out with the highest intentions, stuff falls through the cracks sometimes.

Thanks, everyone.

A natural crystal of a pure element that had isotope concentrations significantly different from typical, should be a very rare occurrence, and possibly important.

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So can we infer that you have found a mineral in some crystal form in an environment that suggests it is not anthropogenic, that you are trying to identify by density?

I believe that micromount specimens of pure silicon exist.

I think 'pure' would be a difficult to assess (especially non-destructively) condition for a natural mineral, especially something as reactive as silicon.....but I don't know that to be true. If you can find a reference to such, or have a compelling reason why it shouldn't be highly improbable, I'd appreciate the education.

Silicon is one of the most abundant elements in the Earth's crust. As you point out the high reactance does make it rare to find in its native form. As you also demonstrate, most people do not know how to identify purity without a destructive test.

So I thought for a moment. Geologists recognize crystal growth patterns as a method to identify purity of an element or compound. A Geologist would also know that an X-ray diffraction measurement will non-destructively verify purity of a crystal. Only a Geologist would find any value in a rare form of an abundant element. So with no profit to be made from these rare specimens I expected only scientific reference citations. I then wondered which Geologist might proudly display a specimen that only another Geologist would appreciate. That led me to the mostly unknown hobby like realm of micro-mount geology. I forgot that these hobbyists prefer to see the look on people's faces when they hand them a mounted sample.

So I've yet to find a micro-mounted piece of native Silicon, but I'm certain at least one exists.

Along my quick search I found that meteoric fulgurite formation can fabricate tiny silicon crystals. (I forgot to save that browsed link.)

The most sensitive technique for the elemental analysis of any material is Neutron Activation Analysis, which analyses down to sub-ppm levels. A sample is first irradiated with neutrons, then the gamma ray emissions from all various isotopes produced, are measured by gamma ray spectroscopy, giving qualitative and quantitative analysis. The method is "non-destructive" but with the proviso that it does remain radioactive for years after. Rather an expensive technique requiring a neutron source to activate the material, but the most sensitive available.

http://en.wikipedia.org/wiki/Neutron_activation_analysis

X-ray Fluorescence Spectroscopy is another technique, but limited to a few ppm detection limit and only surface analysis.

It is quite an accommodating definition of 'non-destructive' that accepts changes as severe as converting some elements into other elements. Spalling, changes in color, embrittlement, and build up of stress from gas inclusions, are also fairly destructive changes.

Thanks for detailing the very logical process by which you came to that conclusion, Redfred.

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I still think it is unlikely a 100% pure sample has been identified from examples found in nature. We differ on the idea of Geologists being able to determine purity from crystal structure.

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'.... Geologists recognize crystal growth patterns as a method to identify purity of an element or compound....'

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Most natural crystals can have interstitial impurities, substitution impurities, or both. Most natural crystals also have some non-impurity defects. In both cases the defects can range from almost imperceptable, to a defining quality. It would be difficult going on the basis of crystal morphology to make useful claims about purity in a range more precise than at least several percent, at best, IMHO.

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'....A Geologist would also know that an X-ray diffraction measurement will non-destructively verify purity of a crystal....'

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I don't think that is correct. If x-ray diffraction is used to determine composition, I'm pretty sure the sample is ground to a powder. I also think that while they can make an absolute determination of the major constituents, the amount of impurities needs to be at least a couple percent to be determined reliably. Once again, that is just going on what I remember, and it is not something in which I am well versed.

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'....Only a Geologist would find any value in a rare form of an abundant element...'

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I'm going to give you a little bit of a hard time about this one. You consider carbon an abundant element, right? ....and it comes in numerous forms, on of the more rare being diamond, right?

It holds true, even if we aren't just talking about pure elements but include abundant compounds....like aluminum oxide.....or should I say, sapphires.

You're confusing powder diffraction spectroscopies with the the function of a silicon monochromator. A nearly pure N doped, mono-crystalline silicon monochromator is the fundamental tool of many X-ray synchrotron beam lines. These man-made crystals can be enormous, multiple kilogram boules of crystal. I know, I've held many in my hand.

Now it comes down to the definition of "pure" and a micro-mount geologist's dexterity to cleave at the impurity to leave an impure and pure remaining crystal to choose to mount in their tiny display box. What you probably don't realize is that sub-milligram crystals are very common in micro-mount displays. Since kilogram crystals are regularly fabricated by people, do you really think nature is incapable of making milligram sized pure crystals that a geologist can identify as pure.

Remember too that X-ray diffraction techniques confirmed what geologists already knew were the crystal structures of the most common crystals. The transparent to visible light crystals did show how their impurities effected the outer layers and shatter/cleaving patterns so that opaque crystals could be similarly identified.

I'll concede I don't know that much about various diffraction spectroscopies. If you tell me there is one capable of non-destructively determining purity of a whole crystal beyond, say 99.5%, I'll take your word for it.

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You leave me unconvinced, though, that visual inspection of crystal morphology is something by which geologists can divine purity accurately and reliably.

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To the question concerning my opinion about the capability of nature to create nearly pure crystals, I have to say that I am convinced it can since I understand man to be part of nature and man has created high purity silicon crystals. But that isn't relevant to our discussion. What is relevant is that I also believe conditions could exit whereby small crystals of pure silicon could form in nature (nature unperturbed meaningfully in that direction by man), but that such formation is so highly improbable especially when restricted to substance that has come to rest in areas within the tangible purview of man, that chances are overwhelmingly against the reality.....not impossible, just highly improbable.

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Now, what do I mean by pure? Pure to me, without qualifiers such as '99.9%' or 'very nearly', is pure in the absolute sense. It would mean a crystal with a lattice structure composed exclusively of silicon atoms (of any non-radiogenic isotopes) with no interstitial impurities other than might be expected to diffuse in at standard atmospheric conditions.

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It is worth noting that when the OP asks about the possibility of pure silicon being found in nature that 100% is the threshold specified in their inquiry.

Only at the single atom level.

I don't know about 100% elemental purity, but one has to define the scope of the sample first. The Chinese manufacture silicon from sand and carbon using electric current to heat the batch to outrageous temperatures, carbon reacting with the oxygen in the silica, and being driven off as a gas. In a volcano, or even at the crust- mantle boundary, such temperatures exist, so why should this reaction not proceed? With extended time for crystallization, remelting and re-crystallization to take place, I should not be surprised to find very large monolithic crystals of "pure" silicon (temporarily ignoring any dissolved metals/nonmetals). Zone melt refining is used by chemists (at times) to purify crystalline materials to the highest levels possible.

'....temporarily ignoring any dissolved metals/nonmetals....'

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Hmmm. Well, okay, if that is how you want to define things. Oh! That reminds me! I have some .... er.... gold, yeah gold, that I'm willing to sell at a very reasonable price for pure gold. The scope of this sale can be set at whatever sample size you wish to define to make this transaction occur. By the standards, you set forth above, it won't have any problem qualifying as pure.

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No, but really, I get your logic. I mean, yeah, of course a volcano could do it if it wanted to. Like you pointed out, even the Chinese can do it, so of course a volcano could too. Good point.