CIBJO releases Gemmological Special Report: considers process of separating measurable facts from opinion; See Gemological Articles below.
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 Post subject: TomAYto - TomAHto?
PostPosted: Mon Oct 02, 2006 11:03 am 
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I was writing out the chemical details of a number of gemstones today, and I noticed something that I thought I woud ask about.

In Gemstones of the World, Beryl is listed as Aluminium Beryllium Silicate and the chemical formula is written as Al2Be3(Si6O18).

In Gemstones by Cally Hall, Beryl is listed as being Beryllium Aluminium Silicate and I've seen the formula listed as Be3Al2(Si6O18).

I'm guessing this is one of those tomayto-tomahto, color/colour things. Is there a specific protocol in writing out chemical formulas, and if so, why am I seeing this written in two different ways?


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PostPosted: Mon Oct 02, 2006 11:29 am 
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I have always heard gem beryl referred to as a beryllium aluminum silicate. Maybe because more elemental substitutions are expected with the aluminum in gem varieties (lithium substitution) than with the beryllium.

It is possible that the beryllium can be replaced with aluminum, but it is my understanding that these specimens do not make desireable gems.

Anyone else on this? Doos?


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PostPosted: Mon Oct 02, 2006 12:03 pm 
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The only times I have read "aluminium beryllium silicate", it has been in connection to emeralds, while it has always been beryllium aluminium silicate about the other beryls. This is with very few accounts taken into the calculation, dunno if it is of any importance or not. What Barbra writes sounds reasonable though.

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PostPosted: Mon Oct 02, 2006 12:12 pm 
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In Gemstones of the world, Beryl is lumped together (as far as the formula goes). On the other hand, Chrysoberyl's formula is marked as Beryllium Aluminium Oxide. So there is probably some reason for the order they have used in both cases.


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PostPosted: Mon Oct 02, 2006 12:19 pm 
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i believe in the IPAC naming convention, the most reactive inorganic element is listed first, followed by what ever it's bound to... This is a chemistry nomenclature exercise, however beryllium is more reactive than aluminum so I think it goes first.


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PostPosted: Mon Oct 02, 2006 2:11 pm 
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Quote:
In Gemstones of the World, Beryl is listed as Aluminium Beryllium Silicate and the chemical formula is written as Al2Be3(Si6O18).

In Gemstones by Cally Hall, Beryl is listed as being Beryllium Aluminium Silicate and I've seen the formula listed as Be3Al2(Si6O18).


Same thing, but I believe jleb is correct.
Be3Al2(Si6O18) is what we use .. which is the same as Be3Al2(Si2O6)3 .


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