[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: Classifying Dar al Gani 140
At 06:34 PM 9/6/98 +0200, you wrote:
>Hello Jeff, hello List,
>
>I am just updating my databases [Oh, how I love this time-consuming,
>never-ending job ! :-( ] and while doing so, I stumbled over DaG 140's
>classification as H3.9-6.
>
>"H3.9-6" - is that a typo or did something escape my attention?
>
>Best wishes,
>
>Bernd
>
Bernd and list,
This is not a typo, but I'm doing my best to eliminate such notation.
Basically,
this is the notation that certain meteoriticists want to use to denote
breccias.
It means that there is a range of petrologic types represented amond the
various
clasts and matrix in the breccia. In the case of DaG 140, at least type
3.9 and type 6
material was observed. I think that this is POOR nomenclature, and I'm
involved
with trying to find a better way. Here are the reasons that it is lousy:
1) The hyphen implies a continuous range, and also implies that there is
no dominant lithology in the breccia. Yet, DaG 140 could be: a) a type 3
chondrite
with a single equilibrated clast found; b) a type 6 chondrite with a single
type 3
clast found; c) a mixture of types 3, 4, 5, and 6 material; a light-dark
breccia with
mostly comminuted matrix and only a few clasts, including type 3 and 6 ones.
So, no matter what I'm interested in, I have no idea if DaG 140 is
interesting.
2) The classification is likely based on one thin section. If somebody else
looks at this breccia and they find a type 3.4 clast, we would have to
reclassify the
meteorite. This could happen A LOT of times for a single meteorite.
3) If the meteorite is like Sharps, a type 3 ordinary chondrite with 1%
CM2 clasts,
how do we name that? H2-3.4? H3.4-CM2? What about Kaidun, a breccia of
CM, CR, EL, EH and God knows what else... CM2-CR2-EL3-6-EH3-4? Ugh.
4) Another meteorite might also be a breccia, but a monomict one. It might
only have type 4 clasts and matrix. It might even be a regolith breccia.
Yet, it would
be classified only as H4.
So, right now we have a literature polluted with this and other nomenclatures
(like using a "/" instead of a "-" for the same thing), and the community
has no
way of looking at a catalog and knowing what's what. The Meteorite
Nomenclature
committee has no jurisdiction over meteorite classification; it just
oversees meteorite
names. It's just a mess.
I plan on publishing my recommendations and a statement about this problem
either
in the next Meteoritical Bulletin, or in that same issue of MAPS as a
refereed paper.
I'm trying to find a concensus among my colleagues right now. I'll post my
suggested scheme on the web for public comments this winter (I'll tell the
list when
this happens).
Comments are welcome.
jeff
----------
Archives located at:
http://www.meteoritecentral.com/list_best.html
For help, FAQ's and sub. info. visit:
http://www.meteoritecentral.com/mailing_list.html
----------
Follow-Ups:
References: