[Rudy Angelo]

A question for all you chemists. I am not much into chemistry as I am actually a ceramicist which has led me to do some research out of curiosity of the material which I use daily (clay). I was told that the formula for the "perfect" clay is
 Al₂O₂ 2SiO₂ 2H₂O as I was looking into this formula I discovered that it is the formula for Kaolinite (plus water) but I also found it most often listed as being Al₂O₃ 2SiO₂ 2H₂O the obvious difference being 2 or 3 oxygen molecules in aluminum. I cant seem to find anything specific as to the difference between aluminum oxides with 2 or 3 oxygen molecules. So I am asking how they might differ and affect the "perfect" clay? Could it be different based on the geological processes that cause the formation of clay from alumina-silicate minerals?

[billnotgatez]

A question for all you chemists. I am not much into chemistry as I am actually a ceramicist which has led me to do some research out of curiosity of the material which I use daily (clay). I was told that the formula for the "perfect" clay is
 Al₂O₂ 2SiO₂ 2H₂O as I was looking into this formula I discovered that it is the formula for Kaolinite (plus water) but I also found it most often listed as being Al₂O₃ 2SiO₂ 2H₂O the obvious difference being 2 or 3 oxygen molecules in aluminum. I cant seem to find anything specific as to the difference between aluminum oxides with 2 or 3 oxygen molecules. So I am asking how they might differ and affect the "perfect" clay? Could it be different based on the geological processes that cause the formation of clay from alumina-silicate minerals?

Welcome to our forum
From WIKI
https://en.wikipedia.org/wiki/Kaolinite

The chemical formula for kaolinite as used in mineralogy is Al₂Si₂O₅(OH)₄,[3] however, in ceramics applications the formula is typically written in terms of oxides, thus the formula for kaolinite is Al₂O₃·2SiO₂·2H₂O.[10] Cement chemist notation is even more terse: AS₂H₂, with the oxides represented as A = Al₂O₃, S = SiO₂, H = H₂O.[citation needed]

I work with pottery a great deal and never seen
Al₂O₂ 2SiO₂ 2H₂O
I usually have seen
Al₂O₃·2SiO₂·2H₂O
Since Oxygen usually has an oxidation state of -2
then in the
Al₂O₂
the Aluminium would have an oxidation state of +2
whereas in the
Al₂O₃
the Aluminium would have an oxidation state of +3
The oxidation state of +3 is the most common for Aluminium (from WIKI)
It would be interesting for you to post a link that says otherwise

I would also note that when you posted your formulas you left out the dot notation between
the silica and alumina and water
This dot represents the special arrangement of the compound.

[Rudy Angelo]

Forgive my oversight in leaving out the dot notation in my formula.
You are right that it is not common and hard to find any reference to kaolinite as
Al₂O₂·2SiO₂·2H₂O
It was one of my ceramics professors that had given me that specific formula.
One of the only other references I am able to find is here.
" natural kaolinite (Al2O2·2SiO2·2H2O)" http://www.ncbi.nlm.nih.gov/pubmed/24794043
It was the discrepancy in what my professor had told me and the majority of information I found that led me to wonder what the difference was and how, if at all it would physically affect the material.

[DrCMS]

According to Wikipedia (and other web info) "The chemical formula for kaolinite is Al₂Si₂O₅(OH)₄ however, in ceramics applications the formula is typically written in terms of oxides, thus the formula for kaolinite is Al₂O₃·2SiO₂·2H₂O"

If you write out both structures you get Al₂Si₂H₄O₉ where as the structure you got from your professor of Al₂O₂·2SiO₂·2H₂O = Al₂Si₂H₄O₈

As there is no such thing as Al₂O₂ I would guess one of you has made a transcription error at some point.

[Rudy Angelo]

As I have noted I am not a chemist nor do I know much about it but I have found some (not much at all) information stating that aluminum can exist as Al₂O₂ apparently called dialuminum dioxide. http://pubchem.ncbi.nlm.nih.gov/compound/16684237
Maybe this is not a natural form of aluminum?
This is all very interesting to me even though I may not understand it completely.
Thank you all for the information and links.

[Borek]

If it exists at all (there are compounds that are listed in databases despite the fact we were never able to synthesize them) it is probably a dimer of AlO, which is itself pretty exotic and was observed only in gaseous phase in very low pressures. Al₂O₃ is the only stable aluminum oxide.

[Rudy Angelo]

That makes sense, Thank you for the clarification.