[meteorite-list] Tafassasset classification

From: fcressy <fcressy_at_meteoritecentral.com>
Date: Thu Apr 22 10:06:54 2004
Message-ID: <001301c26a9a$cfb13440$02611c43_at_pavilion>

Hi John and all,

I believe that, in general, primative achondrites are no longer chondrites
in that the rock has rxperienced melting and chondrules are no longer
present. The rock has recrystallized and it has a crystalline texture.
However, compositionally they remain the same as the parent chondrite
material. So texturally they are achondrites, compositionally they are
chondrites. If I remember correctly from my acapulcoite samples, a lot of
metal is present between the crystals. In a regular differented achondrite,
the metal has separated out as has other material and the resultant
composition of the rock is significanrtly different from the parent body.
As for the difference between a petrographic grade 7 and a primative
achondrite, I agree that this line is fuzzy. Grade 7 chondrites should still
have relict chondrules present. However, I believe that at least one
acapulcoite (NWA725) also contains relict chondrules.
This is my understanding of the subject. Hope it helps a bit but feel free
to correct me if I'm not understanding this correctly.
Regards,
Frank

----- Original Message -----
From: John Divelbiss <j.divelbiss_at_worldnet.att.net>
To: fcressy <fcressy_at_prodigy.net>; Norbert Classen <trifid@timewarp.de>;
Bernd Pauli HD <bernd.pauli_at_lehrer.uni-karlsruhe.de>; Svend Buhl
<svendbuhl_at_web.de>
Cc: <meteorite-list_at_meteoritecentral.com>
Sent: Wednesday, October 02, 2002 8:19 PM
Subject: Re: [meteorite-list] Tafassasset classification


> Frank,
>
> I understand the description of the primitive achondrite...including the
> types you mention.
>
> From that statement in Nortons book, they are still chondrites...just
> overdone a bit. What line did they cross to be called achondrites? And how
> does it relate to Tafassasset being also called a CR7?
>
> John
>
> ----- Original Message -----
> From: "fcressy" <fcressy_at_prodigy.net>
> To: "John Divelbiss" <j.divelbiss_at_worldnet.att.net>; "Norbert Classen"
> <trifid_at_timewarp.de>; "Bernd Pauli HD"
> <bernd.pauli_at_lehrer.uni-karlsruhe.de>; "Svend Buhl" <svendbuhl@web.de>
> Cc: <meteorite-list_at_meteoritecentral.com>
> Sent: Wednesday, October 02, 2002 10:55 PM
> Subject: Re: [meteorite-list] Tafassasset classification
>
>
> > Hello John and all,
> > Regarding your primative achondrite question, Norton's "Encyclopedia of
> > Meteorites" has a page dedicated to the subject (P. 165). He states that
> > "primative achondrites have achondrite textures but still retain
something
> > of their chondritic composition." and that they "are transitional
between"
> > chondrites and achondrites. As examples of primative achondrites, he
uses
> > acapulcoites, lodranites and winonaites.
> > Hope this helps.
> > Frank
> >
> >
> >
> >
> > ----- Original Message -----
> > From: John Divelbiss <j.divelbiss_at_worldnet.att.net>
> > To: Norbert Classen <trifid_at_timewarp.de>; Bernd Pauli HD
> > <bernd.pauli_at_lehrer.uni-karlsruhe.de>; Svend Buhl <svendbuhl@web.de>
> > Cc: <meteorite-list_at_meteoritecentral.com>
> > Sent: Wednesday, October 02, 2002 5:05 PM
> > Subject: Re: [meteorite-list] Tafassasset classification
> >
> >
> > > Hello All,
> > >
> > > Primitive is primitive! Help me to understand the differences
> > please.
> > >
> > > Is the argument about where the line(s) should be drawn between a
> > chondrite
> > > (that is "really" differentiated...like a 7) versus a primitive
> achondrite
> > > (that is not quite differentiated enough to be called a achondrite)?
> > >
> > > Is there really a 7 category and why?
> > >
> > > Are primitive achondrites now considered differentiated enough to be
> > > distinguished from a highly changed chondrite? small versus coarse
> grains
> > in
> > > matrix?
> > >
> > > How is this line drawn? mineral makeup, level of glass, age, grain
> > > size/changes, etc. ?
> > >
> > > Lots of questions with this story.
> > >
> > > Alain would have something to say about all this. Ann Black, is there
a
> > > position written from his corner?
> > >
> > >
> > > John
> > >
Received on Thu 03 Oct 2002 01:07:34 AM PDT