[meteorite-list] Tagish Lake, CH, and Bencubbin-like meteorites

From: Larry Harrison <harrison_at_meteoritecentral.com>
Date: Thu Apr 22 09:42:01 2004
Message-ID: <3A685197.A9E8F743_at_4scope.com>

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 09:39:19 AM PST