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: [email protected]
website: http://cosmochemists.igpp.ucla.edu/Rubin.html
----- Original Message -----
From: "Peter Scherff" <[email protected]>
To: "'Adam'" <[email protected]>
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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