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Horst,

Many of the references in the literature of the diatremes of the Four
Corners region of the U.S. refer to garnet xenocrysts from the mantle
containing oriented exsolved rutile in pyropic garnets. In the paper
on another subject by me and Armand Chase (1961) there is a
photograph of a thick section of one of these. A number of papers by
the late Tom McGetchin are material to any discussion of these
xenocrysts. Also Eric Essene and colleagues have done considerable
recent work on these xenocrysts. Eric has my thick section of the
photographed xenocryst referred to above and has discovered other
minerals that exsolve as oriented extensions of the oriented rutiles.
I hope this helps.

John Rosenfeld

*****
See Figure 4 on p. 529 in:

1961  Rosenfeld, John L. and Armond B. Chase.  "Pressure and
Temperature of Crystallization from Elastic Effects Around Solid
Inclusions in Minerals?," Amer. Jour. Sci., 259, p. 519-541.



>Dear Listmembers,
>
>Granulite facies garnets often show relatively high Ti contents in their
>cores and zonations to nearly Ti-free rims. Sometimes one can find
>finegrained rutile needles inside the garnets in strong orientation. Both
>features may be results of higher solubility of Ti in garnet at high
>pressures (or high temperatures?).
>I was searching for a reference dealing with Ti solubility in garnet, but
>did'nt find anything. Help!
>
>thanks in advance!
>
>horst
>
>=================================
>Horst Marschall
>Mineralogisches Institut
>Universitaet Heidelberg
>INF 236
>69120 Heidelberg
>++49-(0)6221-546021
>[log in to unmask]
>=================================

--
John L. Rosenfeld
Department of Earth & Space Sciences
University of California, Los Angeles
Los Angeles, California  90095-1567

Phone: 310-825-1505
e-mail: [log in to unmask]
website: <http://www.ess.ucla.edu/facpages/rosenfel.html>