Martin wrote:
"Where one has to say, that it's maybe too early to say that, Because
the classification with decimal places, (even with two!), is a
relatively new occurrence..."
Dear Martin,
Your comment sounds to me like the hungry man's dubitable evaluations
of the quality of the the world's leading pancake expert, which
persisted until he ate his fill of her goodies.
Ref: "The Perfect Pancake" by Virginia Kahl http://tinyurl.com/ygjnju6
There are many parallels between say, beach combing and meteorite
collecting. While beauty is in the eye of the beholder and a thousand
and one contortions of the word "rarity" can and will be made by the
interested, I would personally say there is tendency of beachcombers to
want shells that are intact, whether it be for aesthetic reasons or
scientific study to best figure out everything from the evolution to
the habits of the mollusk who created his shell. The case is similar
with meteorites. Jeff's comment (as did mine) referred to the
scientific value of pristine examples which have not been cooked or
watered down. That is undeniable for those interested in the question
of genesis. Jeff and I have side-stepped the question of "rarity".
Personally I think it is moot here. If someone wants to study something
else like an LL3/LL4 smash up, or all the power to them regarding
"rarity" claims, since, like Semarkona LL3.00, only one of them appears
in the database.
Without considering Plutoing the R-chondrites, and with all respect
that each meteorite is unique in its own way, here´s the overview on
LL3 classification:
LL's are the rarest of the H-L-LL tribe (representing only 14%),
LL3 represents only 0.8% of OC's, the least frequent in the database.
Petrological grade 3's of any type (H-L-LL) are also the "rarest"
well-established classification - just 5%.
That would make LL3 a natural regarding "rarity", above and beyond its
scientific desirability to leading researchers like Jeff. Again the
words "holy grail" for OC's come to mind. The association of low
petrological grade (3) with scarcity for recovered meteorites is only
being extrapolated to the extreme with Semarkona, and is of very
arguably special scientific value:
Here´s the current LL3 situation in numbers:
Type # %LL's
LL3.X or LL3.XX 157 58.58%
LL3 102 38.06%
LL3-XX 8 2.99%
LL3/4 1 0.37%
To the point: As you can see, there is plenty more than a natural human
inclination towards perfection (with respect to raw sampling of the
unaltered first meteorites to condense from the soup) in the database
to argue that a LL3.00 or LL3.01 is hard to to find. I´m hopeful you
are right and more "most primitive" OC's are found as classification
gets more complex, but the tendency that many will be is just not there
if you look over the numbers so far covering (in this case) over half
of all LL3's.
If you want to say, for example, the "rarest" is the "H7"
classification - all nine of them- such as NWA 2898, I won't argue.
Many scientists have purposefully avoided that classification which is
another story. It just depends where your interests lie and all
meteorites have their unique story. I don't think we can look at this
as a bell curve with a 3 end and "7" end as the tails, though. If we
hypothesize that there is an OC-type origin point I hope we are having
a go at a singularity and elucidation of commonality In the
Beginning... I know, most of us would rather remain on the fence eating
all flavors of pancakes :-) ... it's such a loaded question ...
Kind wishes, and happy holidays
Doug
-----Original Message-----
From: Chladnis Heirs <[email protected]>
To: [email protected]
Sent: Wed, Dec 16, 2009 8:27 am
Subject: Re: [meteorite-list] Ordinary chondrites - rarest to the most
common classes
Indeed,
it's for the first time, that I read that R-chondrites are included in
the
OC-group. If so, why exactly them and not the K-chondrites, the
Carbonaceous
from grade 3-6, the ungrouped and the enstatite chondrites too?
valuable type of OC from a
scientific perspective is petrologic type 3.00-3.01
Where one has to say, that it's maybe too early to say that,
Because the classification with decimal places, (even with two!), is a
relatively new occurrence - most classifiers seems still to prefer to
use a
simple "3" - so that in case, there are still a lot known type-3ers
awaiting
to be revisited regarding the degree of their (un)equilibration.
But I agree - "Ordinary" is a somewhat misleading term,
- as the ordinary chondrites have told us most about the origin and
formation of the solar system, the planets and ourselves, more than any
iron
or any lunar rock!
Keep that always in mind, if you are tempted, now in the end of the
desert-era and the decreed end of meteorite finding in so many
countries,
with all their weird and fancy exotic types, to wrinkle your nose about
the
"ugly" ordinary 25$-a-kilo-chunk from NWA-wonderland!
Rare as brilliants they are - and they were our beginnings!
Happy holidays to all!
Martin
-----Ursprüngliche Nachricht-----
Von: [email protected]
[mailto:[email protected]] Im Auftrag von Jeff
Grossman
Gesendet: Mittwoch, 16. Dezember 2009 11:33
An: Meteorite-list
Betreff: Re: [meteorite-list] Ordinary chondrites - rarest to the most
common classes
I agree with Doug... the rarest and most valuable type of OC from a
scientific perspective is petrologic type 3.00-3.01, from any of the
chemical groups. Only one is known... Semarkona. If we take a more
expansive definition of "ordinary chondrite" than most of my rather
conservative colleagues are normally willing to accept, I would say
that
the rarest group of OCs is the R chondrites (only ~100 are known and
many of those are paired). In addition, a number of unique ungrouped
meteorites are OC-like. But again, I don't know of any colleagues who
agree with me that R chondrites are in the OC class. [I would say that
the OC class has two clans, the H-L-LL clan and the R clan].
Jeff
Mexicodoug wrote:
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 <[email protected]>
To: [email protected]
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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--
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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