Re: Skeletal apatite again

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Clive:  we never measured Ca/P ratios, we were only concerned about Sm and
Nd isotopes.  Yes, conodonts are very LREE enriched, but the question I
have to ask is, is Nd picked up preferentially over Sm and would this
really make any difference to the isotopic ratio (I think not but I don't
know if its ever been looked at).  Judith Wright did with a microprobe
where she looked at REE pattern variation along an element.  She found that
substitution was governed by ionic radii (Nd and Sm show peaks), resulting
in the concave REE pattern.  I need to look more closely at her graphs but
she seemed to find differences in the relative abundance of certain
elements along an conodont element.
For those of you who don't have this reference it is in Skeletal
Biomineralization: Patterns, Processes and Evolutionary Trends, Volume 1.
J. Carter, ed.

Now there are some papers during the last few years on modeling
partitioning of REE in PO4's and Zhong and Mucci have a new paper out in
Geochimica on REE partitioning between calcite and saturation seawater
solutions.  Its experimental and may not be applicable to nature, but an
interesting read nonetheless.

With respect to crystal distortion effects, I'm not sure but I I would
suspect it being very rare with the REE due to lanthanide contraction, but
hey I'm not a structural chemist.

I'm sort of interested in ionic bonding strength once Nd and Sm (or any
trace element) is in there.  Since the bonding with Nd at least is "tight"
is there any chance of flux out of the lattice to be replaced by something
else?  Again, I doubt it but it would be interesting.

There is a major conference here in Victoria this summer (GAC/MAC) and I
noticed that there are a couple of REE talks in the
mineralogy/crystallography session.  One might be of interested and the
authors are Fleet and Pan, Site Occupancies and Intercrystalline
Partitioning of REE: Apatite and Cuspidine.  It might be worth going into
the literature to see if they have published anything, although its not
biogenic.

I know that there are alot of icthyolith people out there and some of you
have done REE and isotope work....what do you think?

Cindy

Cindy Wright
School of Earth and Ocean Science
Box 1700
University of Victoria
Victoria, British Columbia
V8W 2Y2