[meteorite-list] chondrules?

From: David Freeman <dfreeman_at_meteoritecentral.com>
Date: Mon Feb 14 23:29:51 2005
Message-ID: <42117AA9.2060200_at_fascination.com>

Dear chondritists;
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 <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
>>>
>> >> Meteorite-list mailing list
>>
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>>>>
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Received on Mon 14 Feb 2005 11:29:29 PM PST