[meteorite-list] Ordinary chondrites - rarest to the most common classes

From: Mexicodoug <mexicodoug_at_meteoritecentral.com>
Date: Wed, 16 Dec 2009 04:19:18 -0500
Message-ID: <8CC4C47FAE1051B-1B34-2687_at_webmail-m067.sysops.aol.com>

Hi Melanie and thanks for the enthusiasm you add to the list ...

Here's a high to low sorting of the "ordinary chondrites", for over
32,000 meteorites:

22.0% L6 ("most common")
19.9% H5
12.9% L5
12.3% H4
11.5% H6
7.8% LL5
4.2% LL6
3.3% L4
2.2% H3
2.0% L3
0.8% LL4
0.8% LL3
0.1% L7
0.1% LL7
0.03% H7 ("least common")

But this "common" and "rare" is a misleading label. That is a harder
question if you look too closely at the deails and consider
inhomogeneous and brecciated ordinary chondrites. That can all become
somewhat unique if you ask the right person. Then there are the motley
crew of ungrouped ordinary chondrites where it is hard to generalize.
Some may be a weak classification while others might truly be weird
("rare").

Just a few notes: the H7, L7, LL7 types are not widely used in the
literature and border on impact melts, so I'd take them with a grain of
salt unless someone goes postal on me in which case they are right in
whatever they say. The way I listed these, the meteorites are counted
by the lowest number and won't show up in the higher thermal
(metamorphosed) levels. In other words, for example, an LL3.8-6 is
counted with the LL3's.

If you have a special meteorite, it can sometimes be a "rarer" type if
you start to split hairs, like H3.8 instead of just grouping it within
the H3's, but there is some degree of arbitrariness to this. The
tendency is that more virgin Solar system stuff (closer and closer
3.00) is more special and like a holy grail ("rare" in a sense) to some
who study that - since it is more representative of the original
material before water and heat were added and did their thing. From hat
we can try to get the proof we need to work out early formation
processes and theorize on the related dynamics happening. By this
logic, and considering it is a very studied meteorite, the precious
meteorite SEMARKONA (LL3.00 or is it 3.01 :-)), a witnessed fall from
India, is rather unique being the only one with that 3.00
classification, which makes it super intact since formation and
especially interesting to experts, and most notably Dr. Jeff Grossman
who reviewed and updated its classification upon careful study.

By another measure, the "common" ordinary chondrite, L5, Canadian
witnessed fall, VILNA, is one of those very few special meteorites that
was imaged during atmospheric entry and a precise orbit was determined.
It was not too far from Buzzard Coulee, and what makes it even more
special is that it was classified from a (although witnesses heard
pieces whizzing around) 94 milligram fragment with fusion crust. The
only other specimen found was a 48 milligram piece! This becomes a wild
anecdote of a meteorite tale when one considers that the bolide passed
directly over the only camera recording the sky for 500 miles (over 800
km) and headed for the newly constructed and world's only UFO landing
site which had been built for the Canadian Centennial exposition in St.
Paul, Alberta, where it showered sparks ("retro-rockets" to some
folks). In case you wondered, I believe the Japanese classified on
Antarctic meteorite with 10 milligrams, if you can believe that!

So what actually makes a meteorite rare can turn into a matter of
semantics and who you ask. Even the scale of 3 to 6 (or 7) is somewhat
arbitrary and just looks for convenient thermally changed cairns along
the path toward melting. So if we went the other way, if H, L, and LL
correspond to only three parent bodies, the frequency of the types
follows:

H 45.0%
L 40.6%
LL 14.3%

Hope this helps a little with that general question!

Kind wishes,
Doug















-----Original Message-----
From: Melanie Matthews <miss_meteorite at yahoo.ca>
To: meteorite-list at meteoritecentral.com
Sent: Tue, Dec 15, 2009 7:01 am
Subject: [meteorite-list] Ordinary chondrites - rarest to the most
common classes


G'mornin' listites,,
What is the least common type of ordinary chondrite, as well as the
most common?



Thanks
-----------
Melanie
IMCA: 2975
eBay: metmel2775
Known on SkyRock Cafe as SpaceCollector09

Unclassified meteorites are like a box of chocolates... you never know
what
you're gonna get!



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Received on Wed 16 Dec 2009 04:19:18 AM PST