Julie,
I dealt with a related subject in the reference below that explored
the general subject of the various mechanisms leading to the origin
of schistosity. Among the examples treated are the famous orbicles in
the granite of Craftsbury, Vermont, that, as I recall if my memory
serves me right, were described in the Nineteenth Century by either
Rosenbusch or Grubenmann and to my knowledge were first mentioned in
the 1861 "Geology of Vermont" by Hitchcock et al. (Vol. 2). These
orbicles demonstrate that not all schistose fabrics rely on a
tectonic origin. My paper also includes a photomicrograph of a garnet
in a staurolite schist from southeast Connecticut that is surrounded
by a reaction shell of biotite having a preferred orientation
parallel to the surface of reaction [this would be like the chlorite
shell around garnet described by Eric Essene in his reply to you].
The principles explored in the paper would apply to any mineral that
has a proclivity to grow with an elongate or planar habit because of
contrasting growth velocities in different crystallographic
directions. One of the fundamental principles underlying the paper is
that of natural selection based on an idea explored by Gross and
Müller in a 1923 paper. Natural selection applies to many phenomena
in the physical world and is not solely a biological principle! I
hope a perusal of my paper is of some help even though it doesn't
specifically apply to "randomly-oriented curved crystals," a
phenomenon I admit to never having observed.
Rosenfeld, J. L. (1985). Chapter 21: "Schistosity" in "Preferred
Orientation in Deformed Metals and Rocks: An Introduction to Modern
Texture Analysis." H.-R. Wenk, ed., Orlando, Academic Press, Inc.:
441-461.
Cordially,
John Rosenfeld
*****
Can any member of our group provide an explanation as to why
amphibole in a metamorphic rock (or, for that matter kyanite, or any
other normally straight elongate mineral) might instead grow as
randomly-oriented curved crystals? (Some of the amphibole curves so
much that groups of crystals forms circles or perhaps spirals in a
thin-section view).
This does not look to me to be a product of
growth-during-deformation. The overall distribution of the amphibole
crystals is random, although that texture has been overprinted a
little by the development of a later foliation.
I have a vague vague recollection that this texture might be related
to the speed of mineral growth(?), but I haven't been able to turn up
a reference.
Thanks in advance,
Julie Vry
--
Julie Vry
Senior Lecturer - metamorphic petrology
School of Earth Sciences
Victoria University of Wellington
P.O. Box 600
Wellington, New Zealand
*** note: phone number change, again ***
phone: +64 4 463 6432
messages: 025 644 5598
fax: +64 4 463 5186
email: [log in to unmask]
http://www.vuw.ac.nz
home: +64 4 576 0463
--
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>
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