[meteorite-list] Glass in meteorites

From: jbaxter112 at pol.net <jbaxter112_at_meteoritecentral.com>
Date: Wed, 25 Jun 2008 09:20:30 -0400 (EDT)
Message-ID: <39209.10.250.10.1.1214400030.squirrel_at_webmail.medscape.com>

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
>
>
> ______________________________________________
> http://www.meteoritecentral.com
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
> http://six.pairlist.net/mailman/listinfo/meteorite-list
Received on Wed 25 Jun 2008 09:20:30 AM PDT