[meteorite-list] Are chondrites sedimentary rocks?

From: j.divelbiss_at_att.net <j.divelbiss_at_meteoritecentral.com>
Date: Thu Apr 22 10:16:37 2004
Message-ID: <20030829115601.585E153544_at_pairlist.net>

Eric, Mark and others,

Since I've opened my novice brain on this subject, I'll try to help this
time. I think the settling process Eric is alluding to can in a sense be
compared to taking a bunch of different size balls/BB shot and placing them
in a container. Shake it a bit and what you have is a more compressed volume
with the little ones filling in around the bigger ones eliminating most of
the voids. When I look at any of my low value LL3's(3.0 to 3.5), I can see
such a distribution...making the settling process quite palatable.

Just a thought,

John
> Hello List
>
> I rarely comment on anything, but I will throw my 2¢ in here. I think
> Dr. Ebel makes a good point. That bit of learning was brought home to me
> when Tim McCoy showed me the Smithsonian's spectacular Semarkona LL3.0
> specimen. I exclaimed that it was "like a sedimentary rock." (I had seen a
> few sedimentary rocks in my many years as a field geologist.) Dr. McCoy's
> response was that it really was a sedimentary rock. I had to agree.
>
> It is true that the Earth-oriented texts describe sedimentary rocks as
> settling out of air or water. But what else besides air and water is there
> on Earth? That misses the point. The operative process is the settling.
> Indeed, the word sediment is derived from a Latin verb that means "to
> settle." I would say that it is not the origin of the grains that counts,
> but the process of deposition--the settling.
>
> The chondrules, mineral grains and glass that make up a chondrite form

> by various processes in space. They "settled" by gravity through the vacuum
> of space to their asteroid destination. The processes that makes them
> rock--induration as a geologist would say--are not that different that
> induration of Earth's sedimentary rocks. From there these rocks were
> metamorphosed (except Semarkona) and some were even melted. They became, in
> turn, sedimentary, metamorphic and igneous rocks--the three basic kinds of
> rocks we know here on Earth.
>
> Eric Twelker
> twelker_at_alaska.net
> http://www.meteoritemarket.com
>
> > From: j.divelbiss_at_att.net
> > Date: Fri, 29 Aug 2003 01:43:18 +0000
> > To: Mark Ferguson <mafer_at_imagineopals.com>
> > Cc: meteorite-list_at_meteoritecentral.com
> > Subject: Re: [meteorite-list] Are chondrites sedimentary rocks?
> >
> > Mark,
> >
> > I totally agree with your thinking on this. I did not intend anyone to think
> > otherwise. My comment last night was only trying to put some kind of spin on

> > what could be the thought process when someone uses chondrites and
> > sedimentary rocks in the same reference. So, I too agree that they are not
> > sedimentary rocks as we know them. I'll let others try to argue if they
> > should even be mentioned in the same context.
> >
> > My apologies to anyone who might have been confused by my comments. My
> > personal belief is that chondrites are formed by a process that is still not
> > completely understood by us earth dwellers. I doubt if it will be. Models are
> > just that...but let's keep trying.
> >
> > John
> >
> >> Hi List
> >>
> >> I just have to comment on this. Sedimentary rock, in any definition found in
> >> geology and petrology books is matter which is laid down by either wind or
> >> water, then compacted over time into a durable rock. This is not how
> >> chondrules formed. Chondrules most likely are a coalescing of minute liquid
> >> droplets into larger droplets which is very different from the sedimentary

> >> process. It would be more accurate to liken it to the formation of a
> >> chondrule to that of a rain drop, but that might well be to simple a process
> >> to adequately describe chondrule formation since there are some high
> >> temperatures and very different pressures indicated . But to use
> >> sedimentation is not even close. Totally different mechanisms are involved,
> >> that much is sure. For anyone to use totally different processes and
> >> mechanisms is wrong for that only corrupts a new persons attempt understand
> >> meteoritics.
> >>
> >> Mark
> >>
> >> ----- Original Message -----
> >> From: <bernd.pauli_at_paulinet.de>
> >> To: <meteorite-list_at_meteoritecentral.com>
> >> Sent: Wednesday, August 27, 2003 2:51 PM
> >> Subject: [meteorite-list] Are chondrites sedimentary rocks?
> >>
> >>
> >>> Martin wrote:
> >>>
> >>>> In the interview, Ebel makes two comments that made me wonder...
> >>>> First, he mentions that "Most meteorites are pieces of asteroids.
> >>>> A very few are comets."
> >>>
> >>>> My question is which "very few"? I figure the usual suspects are Orgueil
> >>>> and Murchison, but some comet experts I have talked with discount them
> >>>> and all other meteorites as being of cometary origin.
> >>>
> >>> .. do not forget Tagish Lake and to some extent Krymka (see David Weir's
> >>> comments on Krymka on his website: " ... This material is enriched in
> >> volatile
> >>> siderophiles such as Ag, Tl, and Bi, and represents a late condensate from
> >>> a metal-depleted region of the solar nebula, possibly related to cometary
> >>> material."
> >>>
> >>>> The second thing that caught my eye was when Ebel said, "Chondrites are
> >>>> really sedimentary rocks made up of dust and then chondrules, these
> >> round
> >>>> droplets that were once molten and now are little beads, many containing
> >>>> glass, which were present in the solar system."
> >>>
> >>> He may have read O.R. Norton's comments in Joel Schiff's magazine:
> >>>
> >>> NORTON O.R. (1998) Are chondrites sedimentary

> >>> rocks? (M! Feb. 1998, Vol. 4, No. 3, pp. 22-23).
> >>>
> >>>> My question here is if chondrites can
> >>>> really be considered sedimentary rocks.
> >>>
> >>> The only references I have about sedimentary meteorites:
> >>>
> >>> TOMEOKA K. et al. (1997) Evidence for early sedimentary
> >>> processes in a dark inclusion in the Vigarano CV3 chondrite
> >>> (Meteoritics 32-4, 1997, A129).
> >>>
> >>> TOMEOKA K. et al. (1998) Arcuate band texture in a dark inclusion from
> >>> the Vigarano CV3 chondrite: Possible evidence for early sedimentary
> >>> processes (Meteoritics 33-3, 1998, 519-525).
> >>>
> >>> BRIDGES J.C. et al. (1998) Traces of Martian sediment in Nakhla
> >>> and other SNC meteorites (Meteoritics 33-4, 1998, A023).
> >>>
> >>>
> >>> Best wishes,
> >>>
> >>> Bernd
> >>>
> >>>
> >>> To: martinh_at_isu.edu
> >>> Cc: meteorite-list_at_meteoritecentral.com
> >>>
> >>>
> >>> ______________________________________________
> >>> Meteorite-list mailing list
> >>> Meteorite-list_at_meteoritecentral.com

> >>> http://www.pairlist.net/mailman/listinfo/meteorite-list
> >>>
> >>
> >>
> >>
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Received on Fri 29 Aug 2003 07:55:59 AM PDT