[meteorite-list] Ghubara Revisited

From: Meteordealer <meteor.dealer_at_meteoritecentral.com>
Date: Thu Apr 22 09:37:34 2004
Message-ID: <005101c06627$b48a63e0$88210304_at_dsl.vz.genuity.net>

  I had a large endpiece of Ghubara a while back, around 3kg, and it had the
light gray patches that everyone is talking about. There were numerous
chondrules within the gray areas but aImost none in the darker matrix. I
also noticed the same thing in a large slab of Plainview, TX. that i had. It
is classified as an H5 but had gray patches within the matrix that were
filled with what appeared to be type 3 chondrules. I have photos of the
Plainview at:
http://meteordealer.tripod.com/plainview3.jpg
http://meteordealer.tripod.com/plainview.jpg

Brad Sampson
meteor.dealer_at_gte.net

----- Original Message -----
From: Bernd Pauli HD <bernd.pauli_at_lehrer1.rz.uni-karlsruhe.de>
To: Meteorite List <meteorite-list_at_meteoritecentral.com>
Sent: Thursday, December 14, 2000 6:00 PM
Subject: [meteorite-list] Ghubara Revisited


> Dan wrote:
>
> > The lighter colored section also seemed
> > to have more defined chondrules.
>
> Bernd responded:
>
> > a regolith breccia with a dark matrix and light
> > clasts. The lighter colored sections have more
> > defined chondrules because there are L3 frag-
> > ments set in an L5 host.
>
> James Baxter (private mail):
>
> > I recently obtained a slice of Ghubara in which the DARK
> > portion appears to be unequilibrated and has prominent
> > chondrules and the light portion looks more equilibrated
> > and has fewer and less distinct chondrules. This seems to
> > be the reverse of what you described.
>
> Hello List,
>
> James' observations are confirmed by a passage from Wasson's 1974 book
> on meteorites [WASSON J.T. (1974) Meteorites, Springer Verlag 1974, p.
> 196]:
>
> "The difference in petrologic grade between xenoliths and host may be
> related to their relative friabilities. The material of lower petrologic
> type was more friable and was comminuted to form the host; the stronger
> materials of higher petrologic type were fragmented, but generally
> survived as larger clasts."
>
> Lower petrologic type obviously implies more chondrules - thus the dark
> Ghubara matrix should show abundant chondrules. James' scanned picture
> clearly shows just that and so does a look at my specimen. Higher
> petrologic type means a higher degree of recrystallization, and,
> consequently fewer chondrules. In a nutshell: The host matrix is
> chondrule-rich, the clasts should be chondrule-poor.
>
> But Dan wrote to the List:
>
> > The lighter colored section also seemed
> > to have more defined chondrules.
>
> Perhaps Wasson can again help (page 196):
>
> "If this explanation is correct, some cases should be found where the
> clast is of lower petrologic type than the host, since the correlation
> between friability and petrologic type is not a perfect one."
>
> Wasson does not mention if such "cases" may occur simultaneously in one
> and the same meteorite (specimen). Does James have the "run-of-the-mill"
> version of Ghubara and Dan the more "exotic" version? Or is Dan
> mistaken?
>
> With the help of a 12x loupe, I took another look at my Ghubara slice
> and noticed about an equal number of chondrules in both "lithologies",
> whereas James' xenolithic component almost seems to be devoid of any
> chondrules; so now I am at my wit's end :-(
>
> Folks, grab your Ghubaras, look at them closely, take your Ghubara thin
> sections and examine them in plane and polarized light and report to the
> list your findings. I think this is a great occasion for this list to do
> invaluable scientific, observational work.
>
> By the way, the entry in the Blue Book also supports James' observation:
>
> "... the host is unequilibrated, with olivine Fa21.6
> to Fa26.5, but olivine of xenoliths is Fa24 ..."
>
>
> Best wishes and
> thank you very
> much James,
>
> Bernd
>
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Received on Thu 14 Dec 2000 06:43:47 PM PST