[meteorite-list] Glass in meteorites

[STARSANDSCOPES at aol.com]

Hi Jeff and Jim,  Wow, tell us more  about the article in Science.  Could it 
be ordered as a single copy at this  point?  Tom


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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