[meteorite-list] chondrules?

From: Norman Lehrman <nlehrman_at_meteoritecentral.com>
Date: Mon Feb 14 23:15:24 2005
Message-ID: <20050215041523.96736.qmail_at_web81005.mail.yahoo.com>

Gerald, Tracy & list,

Sorry for the slow reply. I'm out in the field, and
probably have no business responding anyway, but your
question is an interesting one. I have worked with
lots of accretionary lapilli in volcanic settings all
over the world. Like Tracy said, I also know of no
chondrules with truly equivalent concentric structure.

However, the general idea of accretionary dust-balls
and condensates in the solar nebula is appealing.
What we would need to do to make the resulting
sphereoids match observations is recrystallization by
one means or another. Many chondrules consist of
single minerals. It might even make sense for some
of the armoring that we see to result from misfit
impurities being expelled from the growing crystal to
its exterior rim.

Understand that my comments are a gross speculation
based on terrestrial knowledge. I have virtually no
familiarity with published chondrule research, so I'm
sure there are others on the list that can offer
better answers.

That said, I would reaffirm that the mental image
suggested by accretionary lapilli is intuitively very
appealing. It must've been something analogous---

Regards,
Norm
(http://tektitesource.com)

--- Gerald Flaherty <grf2_at_verizon.net> wrote:

>
> Subject: Re: [meteorite-list] a question about
> chondrules
> I'm reposting this as I received only one response.
> Please reply if you
> have any thoughts on this question. Thanks a lot in
> advance3.
>
> > ON THE ORIGIN OF CHONDRULES
> > Norm and List,
> > Please excuse my ignorance for putting forth this
> question but as a
> > relative "newbe" to meteorite collecting, I hope
> you will entitle me to
> > this query.
> > I came across the term "accretionary lapilli" also
> called "volcanic
> > pisolites" in Dorothy Ferris Lapidus 1987 edition
> of "The Facts on File
> > Dictionary of Geology and Geophysics.
> > If you bear with me I'll quote " these are
> shperoidal concentrically
> > layered pellets composed mainly of vitric dust and
> ash, usually between 2
> > and 10 mm in diameter. They are formed primarily
> through the accretion of
> > ash and dust by condensed moisture in eruption
> clouds. Formless nuclei of
> > coarse particles fall through the fine debris and
> acquire shells of
> > progressively finer ash. These concentric shells
> indicate the increasiing
> > temperature and decreasing humidity of the cloud
> at lower levels.
> > My question is, does the process described above
> provide any
> > anology("something similar but different") to the
> origin of chondrules.
> > A solar nebula is obviously different than a
> volcano but is there any
> > analagous sympatico to the spheroidal shape?
> > I've seen neither a macro nor micro view of a
> cross-section of a
> > chondrule so I can't speak to the issue of
> concentric layering.
> > Please excuse this question if it either "offers a
> keen grasp of the
> > obvious" or is so "out of the ballpark",
> "continent", "planet", "sun
> > (star) system", "gallaxy" (that's as limiting as
> my current unaided memory
> > allows my imagination to propel itself).
> > Thank you for your indulgence.
> > Jerry Flaherty
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Received on Mon 14 Feb 2005 11:15:23 PM PST