[meteorite-list] Type 7 chondrites

[Alan Rubin]

Most classifiers don't use the type-7 designation because many of the 
chondrites that have been called type-7 seem to be impact-melt breccias. 
Most researchers believe that thermal metamorphism probably caused by 
asteroidal heating engendered by the decvay of short-lived radionuclides 
like 26-Al heated chondrites from type 3 to 4 to 5 to 6.  If shock was 
responsible for causing a rock to be called type 7, then it seemed more 
prudent to just call it shocked and not use the type-7 designation.  Most 
researchers believe that the primitive achondrites were also partly (or 
completely) melted by heating caused by the decay of 26-Al.  I am not of 
these camps; it seems to me that heating of chondrites from type 3 to type 6 
also results from impact heating and that the primitive achondrites formed 
in an analogous way, but that is another story.
Alan


Alan Rubin
Institute of Geophysics and Planetary Physics
University of California
3845 Slichter Hall
603 Charles Young Dr. E
Los Angeles, CA  90095-1567
phone: 310-825-3202
e-mail: aerubin at ucla.edu
website: http://cosmochemists.igpp.ucla.edu/Rubin.html


----- Original Message ----- 
From: "Peter Scherff" <PeterScherff at rcn.com>
To: "'Adam'" <meteorite-list at meteoritecentral.com>
Sent: Monday, March 04, 2013 3:14 PM
Subject: [meteorite-list] Type 7 chondrites


>
> Hi,
>
> Is there any consensus about petrologic type 7 chondrites? Are they better
> classified as Primitive Achondrites? If type 7 is different from primitive
> achondtites what is the line between them?
>
> Thanks,
>
> Peter Scherff
>
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