Forwarded: F in skeletal apatite

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Just thought I'd forward this and see what happens

Date:          Wed, 23 Nov 1994 21:28:13 +0100 (NFT)
From:          Ivar Puura <Ivar.Puura@pal.uu.se>
Reply-to:      Ivar Puura <Ivar.Puura@pal.uu.se>
Subject:       F in skeletal apatite
To:            BIOGENIC APATITE DISCUSSION <cwright@sal.uvic.ca>, dlc@geology.wisc.edu, 
               glnct@bristol.ac.uk, map2@leicester.ac.uk, wriedel@ucsd.edu


Dear colleagues,

Puzzled by strange messages from the paleonet server, I am
slightly hesitant to post a longer message there.

If skeletal apatite discussion is going on somewhere in a smaller 
circle, I hope it would be possible to join. I am posting this
to everyone who has discussed aspects related to biogenic apatite
in PALEONET.

As Dr Mark Purnell has touched a subject closely related to our 
X-ray diffraction study in progress on mineralogy of fossil and Recent 
skeletal apatite, I would use this opportunity to introduce myself, 
in a hope of new contacts.

I am working with Cambrian and Ordovician 
lingulate brachiopods from Estonia and Sweden, 
presently as a PhD student at Uppsala University.

One aspect related to this study is documenting the variation in 
lattice parameters of apatite from lingulate brachiopod shells
from a variety of sedimentary/diagenetic environments 
over geological time scale. 

A similar project on fossil and Recent vertebrates, including
Devonian fishes, has been just started by Estonian colleagues. 

As a work hypothesis, the following statements on composition
of skeletal apat ite in vivo and an expected trend of post-mortem 
change were accepted.

(1) Skeletal apatite of Recent lingulate brachiopod shells is F-
containing carbonate hydroxylapatite. Roughly, the same apatite 
species occurs in Recent vertebrate teeth and bones. 

(2) In vivo, the lattice of skeletal apatite contains OH-anions 
in the positions where F-anions can substitute. It has been 
suggested that substitution of OH- by F- is initiated in vivo, as 
skeletal tissue (of shells, bones or teeth) loosing the contact 
with generating organic matrix "maturates" by substitution of OH- 
by F- (e.g., Lucas and Prevot, 1991). Variations in lattice 
parameters of skeletal apatite in Recent organisms may be partly
related to this phenomenon and partly to changes in metabolism 
during life, as shown by studies of human bone and teeth.

(3) Most common post-mortem substitutions are the replacement of 
OH- by F- and PO43- by CO32- and F-. It has been suggested (e.g., 
by Slansky, 1986) that for maintaining electrochemical balance, 
incorporating carbonate to the lattice is correlated to some 
additional incorporation of fluorine.
    Thus, roughly, fossil skeletal apatite is close to 
carbonate-fluorapatite (syn. francolite), with higher carbonate and 
fluorine content than skeletal apatite generated in vivo.
--------------------------------------------------------------
-

Our preliminary results indicate that these assumed general
trends may be biased by many factors. For instance, in many 
cases, organic matter in fossils may have been 
replaced by secondary, presumably bacterially-mediated carbonate-
fluorapatite. In this case, a fossil sample may be a composite of 
different apatite phases of different origin.
     Possible presence of different apatite phases cannot be 
distinguished by standard X-ray analysis, catching a 
composite signal from a fossil apatite sample.
     Therefore, for amplifying and separating the signals from 
close phases of fossil apatite, XRD measurement regime and 
data-processing software designed especially for 
these apatite studies was developed.
     We hope, this approach, combined with other methods, allows
to estimate roughly the proportions of "primary" (but altered) skeletal and 
secondarily precipitated apatite phases present in fossil 
skeletons and can serve as a critical test before using the material 
for, e.g., stable isotope or REE studies.

I would appreciate any information from colleagues and research groups 
dealing with close topics, or interested in further information exchange.

Please reply to e-mail address Ivar.Puura@pal.uu.se

Thank you in advance,

Sincerely,

Ivar Puura
Institute of Earth Sciences
Uppsala University
Norbyva"gen 22
Uppsala S 75236 Sweden
FAX +46 18 182749
e-mail Ivar.Puura@pal.uu.se





Dr Mark A. Purnell

Department of Geology, University of Leicester
University Road, Leicester LE1 7RH, U.K
tel: 0116 2523629  fax: 0116 2523918