[meteorite-list] Tagish Lake, CH, and Bencubbin-like meteorites
From: Mike Farmer <farmerm_at_meteoritecentral.com>
Date: Thu Apr 22 09:42:01 2004
GOOD LUCK! I spent over a month up there just after the fall and all I have is a .4
gram fragment. The Canadians even demand the tiny miligram size fragments that they
loaned out back.
I doubt you will ever even see a 1 gram slice.
Larry Harrison wrote:
> Greetings List,
> Is there any Tagish Lake available to collectors. I would like to purchase about
> a 1 gram slice.
> Larry Harrison
> Jeffrey N. Grossman wrote:
> > There is no formal procedure for meteorite classification schemes to
> > be accepted. Only passage into common use among researchers constitutes
> > acceptance. The "5-member" rule you may have heard about, stating that
> > 5 meteorites with identical heritage are needed to define a group,
> > was proposed by John Wasson, and has evolved into a tradition. But it
> > is also not a formal rule of any kind, as there are no formal rules
> > nor any group with authority to make rules formal.
> > As for Tagish Lake, there has only been one formal publication on it so
> > far, the original Brown et al. article in Science, and the authors said:
> > "We tentatively conclude that Tagish Lake is a new type of carbonaceous
> > chondrite. We note, however, that there are no examples of CI2 chondrites,
> > and we do not rule out the possibility that Tagish Lake's unusual chemical
> > and isotopic characteristics are due to its being a less altered CI
> > chondrite."
> > In the Bulletin, I called it "C2, ungrouped." As this is fully
> > consistent with Brown et al., I'd recommend using this until some
> > other classification develops in the literature.
> > There has also been discussion in this list about "bencubbinites" and CH
> > chondrites. What you have with these meteorites is basically science
> > in flux. It's clear that meteorites called CH and bencubbin-like (or
> > B or CB chondrite) are related to the CR chondrite clan. However nobody
> > has written the definitive paper delineating the properties of these
> > groups and differences with other groups. Both CH and Bencubbin-like
> > meteorites are heterogeneous in their physical and chemical properties.
> > The fuzziness in these groups is illustrated by abstract titles like
> > Sasha Krot wrote last year: "Chondrules of the very first generation
> > in Bencubbin/CH-like meteorites..." In fact, some people (myself
> > partially included) are even skeptical that these are all chondrites,
> > as opposed to what Wasson and Kallemeyn (1990) called "subchondritic."
> > The lists posted by others to this group saying which meteorites were CH
> > and which were Bencubbin-like are accurate. However, take all these
> > classifications with a grain of salt until researchers start to converge
> > on a common nomenclature. For now, my recommendation is to call them
> > "CH chondrites" and "Bencubbin-like meteorites." But that's just my
> > opinion at this moment in time.
> > jeff
> > p.s. The "type" CH chondrite was Allan Hills 85085. The name was introduced
> > by Bischoff et al 1993 (GCA paper). I don't know why they chose "CH"
> > meaning high metal over "CA" for Allan Hills or Acfer, as would be the
> > traditional way of naming C chondrite groups, but it caught on
> > and has never been countered.
> > 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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Received on Fri 19 Jan 2001 10:56:31 AM PST