I thought I would chime in a moment. Our oolites that are calcium carbonate acretions have layering and concentric structures. After the silica replaces the calcium carbonate, they are quite interesting, hard and worthy of thin slice work.
Dave F.
Norman Lehrman wrote:
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 <[EMAIL PROTECTED]> 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.
question but as aON THE ORIGIN OF CHONDRULES Norm and List, Please excuse my ignorance for putting forth this
you will entitle me torelative "newbe" to meteorite collecting, I hope
called "volcanicthis query. I came across the term "accretionary lapilli" also
of "The Facts on Filepisolites" in Dorothy Ferris Lapidus 1987 edition
shperoidal concentricallyDictionary of Geology and Geophysics. If you bear with me I'll quote " these are
ash, usually between 2layered pellets composed mainly of vitric dust and
through the accretion ofand 10 mm in diameter. They are formed primarily
clouds. Formless nuclei ofash and dust by condensed moisture in eruption
acquire shells ofcoarse particles fall through the fine debris and
indicate the increasiingprogressively finer ash. These concentric shells
temperature and decreasing humidity of the cloud
at lower levels.
provide anyMy question is, does the process described above
anology("something similar but different") to the
origin of chondrules.
volcano but is there anyA solar nebula is obviously different than a
cross-section of aanalagous sympatico to the spheroidal shape? I've seen neither a macro nor micro view of a
chondrule so I can't speak to the issue of
concentric layering.
keen grasp of thePlease excuse this question if it either "offers a
"continent", "planet", "sunobvious" or is so "out of the ballpark",
my current unaided memory(star) system", "gallaxy" (that's as limiting as
allows my imagination to propel itself). Thank you for your indulgence. Jerry Flaherty
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