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Hi Robert,

Indeed, my concern was misunderstanding, while my guess was your intention
was different from that. My reaction, seen by some as a strong one I think,
is just because we require to keep the basics clear and properly presented -
nto always easy as I know myself quite well.
Thanks for your response, I appreciate it. So, let's keep this for 'solved'
than.

Best,
Pier.





> From: Robert van Geldern <[log in to unmask]>
> Reply-To: Stable Isotope Geochemistry <[log in to unmask]>
> Date: Mon, 26 Jul 2010 11:35:28 +0200
> To: <[log in to unmask]>
> Subject: Re: [ISOGEOCHEM] 25*C and SI in concrete
> 
> Hi Pier,
> to make a long story short:
> My comment is strictly correct only for calcite using NBS 19 as a reference
> material, of course.
> Not for other carbonates and not for mixtures.
> 
> 
> the long version:
> Indeed my comment
> 
>> You can run your carbonates at any temperature you want as long as your
>> temperature is _constant_  (in case of 18O analysis) for your standards and
>> your samples.
> 
> can be misunderstood in a way that this refers to any carbonate (calcite,
> dolomite, ankerite etc.) or even carbonate mixtures. That, of course, is not
> the case. The original question from Andrew did not point out what carbonate
> should be analyzed. However, in most cases labs deal with calcite and since
> NBS 19 is also a calcite this simplifies things to the IT principle and
> constant temperature. Willis answer already pointed out the problem with 18O
> and carbonate mixtures in more detail. Running mixtures you have to take care
> about the different fractionation factors at different temperatures for the
> minerals in the sample and have a look into the already cited Rosenbaum and
> Sheppard (1986) or Sharma and Clayton (1965). In case of such mixtures you
> should also think about methods to react your minerals separately and you
> pointed out this in detail. Thanks.
> 
> What I am by far more concerned about is the fact that the real composition is
> sometimes not known in a lot of cases. As long as samples come from limestones
> or fossils you will have an idea about calcite, dolomite or aragonite but for
> other sediments you have to run XRD on your material before any isotope
> analysis. Obviously it should be the first step to know what is analyzed but I
> have seem a couple of projects being not aware of this fact. Just to keep this
> in mind.
> 
> Thanks for the concrete references.
> Are you aware of any fractionation studies of minerals associated with
> portland cement reaction type?
> 
> regards,
> Robert