[meteorite-list] petrological type

From: Alan Rubin <aerubin_at_meteoritecentral.com>
Date: Sat, 12 Apr 2014 12:39:51 -0700
Message-ID: <055201cf5686$fa710130$ef530390$_at_ucla.edu>

Important meteorites should be well described and a lot of info should be
available in the detailed characterization. For now, most people are
comfortable with just the group/type designation with all other measured
parameters and interpretations being left for the detailed description. You
can rest assured that not every researcher would agree that Semarkona has
been aqueously altered to an extent equivalent to a 2.8 especially since
such a scale for ordinary chondrites is currently undefined. What is needed
is the demonstration that ordinary chondrites have been aqueously altered to
different extents, the numerical breakdown into different degrees of
alteration and an unambiguous definition of what each stage designates. No
one has done this and it would be hard. What we have now a number of
observations: e.g., (a) the Semarkona matrix contains some smectite, (b) the
opaque phases in the Semarkona matrix generally lack kamacite and instead
consist mainly of carbide, Ni-rich metal, pentlandite, troilite and
magnetite, (c) many type-3 OC contain RP and C chondrules that have bleached
rims reflecting aqueous alteration, (d) hydration of glass in some Semarkona
chondrules, and (e) alteration of some chondrule mesostasis regions. Other
type-3 OC are more poorly studied than Semarkona and we are quite far from
creating a comprehensive alteration scheme.

Alan Rubin
Institute of Geophysics and Planetary Physics
University of California
3845 Slichter Hall
603 Charles Young Dr. E
Los Angeles, CA 90095-1567

office phone: 310-825-3202
fax: 310-206-3051
e-mail: aerubin at ucla.edu
website: http://cosmochemists.igpp.ucla.edu/Rubin.html

-----Original Message-----
From: meteorite-list-bounces at meteoritecentral.com
[mailto:meteorite-list-bounces at meteoritecentral.com] On Behalf Of Jim
Wooddell
Sent: Saturday, April 12, 2014 12:08 PM
To: meteorite-list at meteoritecentral.com
Subject: Re: [meteorite-list] petrological type

Hi Alan and all,


Is not the description/s part of the classification so that the researcher
can better describe what is found without having to baffle over a number or
preset definition that might...kind of...come close to what is found??

Jim

On 4/12/2014 10:01 AM, Alan Rubin wrote:
> Since Van Schmus and Wood (1967), the group/petrologic type
> designation has been entrenched (i.e., LL3.0, H4, L6), that it would be
impossible to purge.
> So, calling Semarkona LL T3 just won't work -- no one would adopt it
> as a new convention. If we wanted to call Semarkona LL3.00 A2.8, that
> might be
>
> okay, but you would have to convince people first that a two-tier
> system is needed. It is probably best to exclude weathering and shock
> stage since we
>
> cannot designate every property in a classification (e.g., average
> olivine
>
> Fa content, cosmic-ray exposure age, oxygen-isotopic composition,
> chondrule size, etc.). A problem of course is that it may be
> difficult to disentangle thermal metamorphism from aqueous alteration,
> leaving a researcher baffled
>
> as to what to designate a particular rock. It would be better to
> leave out a classificatory parameter and to just guess and have the
> rock misclassified.
>
> Alan Rubin
> Institute of Geophysics and Planetary Physics University of California
> 3845 Slichter Hall
> 603 Charles Young Dr. E
> Los Angeles, CA 90095-1567
>
> office phone: 310-825-3202
> fax: 310-206-3051
> e-mail: aerubin at ucla.edu
> website: http://cosmochemists.igpp.ucla.edu/Rubin.html
>

--
Jim Wooddell
jim.wooddell at suddenlink.net
http://pages.suddenlink.net/chondrule/
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Received on Sat 12 Apr 2014 03:39:51 PM PDT