[meteorite-list] Dr. Jeffrey N. Grossman Chondrule paper in Science

From: STARSANDSCOPES at aol.com <STARSANDSCOPES_at_meteoritecentral.com>
Date: Thu, 26 Jun 2008 00:34:07 EDT
Message-ID: <c6c.286eb171.3594763f_at_aol.com>

Hi list, I just read Jeff's paper on chondrule and chondrite formation.
I'm still trying to get my brain around some of the points.

Well done!!! A whole new way of looking at everything!

I had a question related to the paper but just a little off topic. It is
directed to Jeff but any one with knowledge in this area should jump in.

The many structures found in chondrules, are they formed during the
condensation process at formation or later during subsequent heating and shock events?

Perhaps both? I often see structures within chondrules that give the
appearance (at least) of having grown out of chemical reactions within the
chondrule. Structures that I can not imagine shock forces having caused.

Tom Phillips

In a message dated 6/25/2008 7:27:00 A.M. Mountain Daylight Time,
jbaxter112 at pol.net writes:
Hi Jeff,

Congratulations on the cover story in Science on formation conditions of
chondrules. Your color photograph of a Semarkona cross section is
fabulous.

Cheers,
Jim Baxter

> I think it is fairly clear that the glass in chondrites, which forms in
> chondrules because of their rapid cooling from a partially molten
> state, is stable on the time-scale of the age of the solar
> system. In the most primitive chondrites, the ones unaffected by
> reheating or alteration on asteroids, the glass is preserved in
> pristine condition to this day. In metamorphosed chondrites, glass may
> survive in protected areas of type 3.9-4 material, but the
> reheating caused most of the glass to crystallize into feldspar early
> in solar system history. In aqueously altered chondrites, like CMs, the
> glass was mostly replaced by phyllosilicates and other phases due to
> the chemical action of water on the asteroid. Water is apparently a key
> ingredient in devitrifying silicate glasses, especially
> important in earth rocks.
>
> The image on Tom's website is almost certainly one of dendrites
> (probably olivine) in what was once glass. These dendrites were the
> result of rapid crystallization during cooling of a chondrule
> melt. Because this is a metamorphosed chondrite, the glass is now most
> likely replaced by fine-grained feldspathic material.
>
> Jeff
>
> At 12:24 AM 6/25/2008, STARSANDSCOPES at aol.com wrote:
>>Hi, Several years ago I ran onto an unusual chondrule in JaH 055
>> that looks like glass but it is forming in crystals. I have had
>> various explanations presented to me and all involved "Glass" This
>> might be "On topic"? If any one is up to taking a look and sharing
>> their observations, I would greatly appreciate it. Just go to my
>> Meteorite Times Micrograph
>>Gallery
>>http://www.meteorite.com/meteorite-gallery/meteorites-alpha_frame.htm
>> and select alphabetical sorting, JaH 055, and then
>>crystal structure. These shots were produced using incident
>>(reflected light). Thanks, Tom Phillips In a message dated
>>6/24/2008 10:02:55 P.M. Mountain Daylight Time, cynapse at charter.net
>> writes: Have any studies been done on "decay" of glasses in
>>meteorites into crystaline configurations? Is there a mesurable
>> rate, or does it not happen? This story brought that to mind-- if
>> impact-generated glasses in meteorites HAVE NOT "decayed" into
>>crystaline material in 4 billion years, it's fairly good evidence
>> that it won't happen "in billions of years", as the story speculates.
>
> 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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Received on Thu 26 Jun 2008 12:34:07 AM PDT