[meteorite-list] Am I missing something here?

[Alexander Seidel]

Hi Jeff,

if this is state of the art of the classification scheme, and has been accepted by a majority of the meteoriticists, does this mean some important primitive meteorites finally need a refinement of their established classifications?

I am thinking of (e. g.) the Krymka meteorite, which to my knowledge is an LL3.1. Does this have to be refined to become either an LL3.05, or an LL3.10, or an LL3.15 in the end?

Just curious,
Alex
Berlin/Germany


-------- Original-Nachricht --------
> Datum: Mon, 16 Jun 2008 07:36:53 -0400
> Von: Jeff Grossman <jgrossman at usgs.gov>
> An: "Dark Matter" <freequarks at gmail.com>, "Meteorite List" <meteorite-list at meteoritecentral.com>
> Betreff: Re: [meteorite-list] Am I missing something here?

> Dear Martin and list,
> 
> I can't comment on the CO3 oxymoron, but I am the inventor of the 
> type 3.05 classification, so I can comment on that.
> 
> As we have studied type 3 chondrites over the last 30 years, 
> especially ordinary and CO chondrites, we have been gradually 
> refining the 1967 Van Schmus and Wood classification scheme.  In 
> 1980, we realized that type 3 chondrites alone showed as great a 
> range of metamorphic effects as type 4-6 did, so Sears and coworkers 
> including me, proposed subdividing type 3 into types 3.0-3.9.  In 
> 2005, Grossman and Brearley (2005) described a similar wide range of 
> metamorphic effects just between types 3.0 and 3.2 and subdivided 
> this into 3.00-3.15 by steps of 0.05.  Since then, we have even begun 
> to recognize different levels of metamorphic heating between types 
> 3.00 and 3.05, and so we find Acfer 094 at type 3.00, Semarkona at 
> type 3.01, ALHA77307 at type 3.03 (e.g., Bonal et al. 2007; Kimura, 
> Grossman and Weisberg, 2008, MAPS in press).
> 
> These differences are quite real and important.  In type 3.05 
> ordinary chondrites, the olivine in chondrules has begun to decompose 
> from its high-temperature state, the matrix chemistry is quite 
> different, especially for sulfur, and the metal has greatly changed 
> in structure and composition (all compared to the much, much rarer 
> type 3.00-3.01 chondrites).  Although these numbers do not tell you 
> the peak metamorphic temperature, they are very useful in describing 
> the various transitions that occur during metamorphic heating.
> 
> The fact that there may be many possible combinations of chemical 
> group and petrologic type is a good thing, although there certainly 
> aren't 1500.  Basically, current usage is 3.00-3.04 (5 categories), 
> 3.05-3.15 (3 categories), 3.2-3.9 (8 catagories), 4-7 (4 categories) 
> = 20 categories.  I suppose if you double this for classifiers who 
> can't make up their minds, you get ~40 categories, times 3 chondrite 
> groups plus 2 transitional groups = ~200 total combinations.
> 
> Jeff
> 
> At 11:24 PM 6/15/2008, Dark Matter wrote:
> >Hi All,
> >
> >Twice in the past few days, I found myself staring at the screen in
> >confused disbelief. The two statements in sales ads:
> >
> >
> >"a yet unclassified CO3"
> >
> >and
> >
> >"absolutely rare type L3.05 !"
> >
> >just seem to me to border on absurdity. How can a unclassified
> >specimen be identified by its classification?
> >
> >And if we carry petrological grade to the hundredths, then
> >theoretically we could have over 1500 ordinary chondrite designations
> >not to mention all the transitional possibilities. I fail to see how
> >that level of hypothetical opinionated hair splitting could do any
> >good...except for ebay sales ads that is.
> >
> >Just an evening though when I should be working on something else.
> >
> >Cheers,
> >
> >Martin
> >______________________________________________
> >http://www.meteoritecentral.com
> >Meteorite-list mailing list
> >Meteorite-list at meteoritecentral.com
> >http://six.pairlist.net/mailman/listinfo/meteorite-list
> 
> Dr. Jeffrey N. Grossman       phone: (703) 648-6184
> US Geological Survey          fax:   (703) 648-6383
> 954 National Center
> Reston, VA 20192, USA
> 
> 
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