[meteorite-list] Red spots on Tatahouines?

From: Mexicodoug <mexicodoug_at_meteoritecentral.com>
Date: Tue, 29 Sep 2009 12:12:35 -0400
Message-ID: <8CC0F36C6CA82E1-F94-2FA00_at_webmail-d013.sysops.aol.com>

Hi Melanie, Werner, Jeff, Bernd and List,

This is yet another reason why cleaning/polishing Tatahouine meteorites
can be shortsighted due to all the exquisite and fragile features it
packs, invisible to the untrained eye.

Plenty of uncleaned Tatahouine specimens still have the Jurassic age
Tatahouine desert sand packed in the nooks and crannies, as well as the
oxidizing iron inclusions.

Most visibly (and I think more likely than calcite), Jurassic sand is
bright red colored, and makes a beautiful "natural" contrast with the
green/gray meteorite and also could be what Melanie is seeing.

The red formed in the limestones basically due to rust staining. The
oxidizing atmosphere of the Jurassic (big-dino) time period interacted
with iron: Forming hematite and weathering basically creating the red
hematite streak as a pigment staining the world in that geological age
(as I understand it).

Based on (Gillet, Barrat et. al. ca. 1993-1999), Bernd wrote:

"Second, yellowish to *light orange calcitic aggregates* were found in
some samples. They mainly occur as a partial filling with a rosette
texture or completely fill some fractures (ca. 100 ?m wide)."

It is worth noting that the calcitic stuff (over 60% calcium carbonate)
was shown to be completely derived from the environment. In other words
it is RESIDUE FROM THE LIMESTONE/SAND, and NOT to be from the meteorite
itself - the basic point of that article. The aggregate
s were said to
have developed during time from the fall to the collection of more
specimens 63 years later.

The "rosette" color Bernd cites, only might occur due to staining of
the typically white calcite with a little bit of the hematite pigment
mentioned. In my personal experience, this is not very obvious upon a
quick look at the specimens and yellow is much more common, that can
blend in easily with the meteorite. (Of course one can't rule out its
staining by the rusting of an iron inclusion that happens to be on the
calcite wetted surface, in which case the iron could be meteoritic).

The suggestion by Barrat and Gillet et. al., was that this occurred due
to aqueous leaching of carbonates from the limestone sands into tiny
cracks (where we can imagine the water being sucked in by
wetting-surface tension). I.e., perhaps water repeatedly entered and
stuck in the optimally thin crevices and repeatedly dried out over the
years, concentrating the carbonates from the 6% of the "soil" to ten
times that amount in the appropriately sized fluid sucking crevices.

The carbonates, in turn, are derived from the calcium carbonate used in
making marine organism shells and maybe a dash of their bones.

So, besides all the wonderful things already said about Tatahouine, we
now know that it is the official meteorite we can collect that itself
enjoys collecting earthly seashells :-)

Here are examples

http:/
/www.diogenite.com/b8y.jpg (Jurassic sand)

http://www.diogenite.com/b6y.jpg (predominantly Jurassic sand glued in
with some carbonates)

http://www.diogenite.com/b11y.jpg (iron inclusion oxidation)

Hope this helps and also a big welcome to Melanie who recently joined
the list.

Thanks kindly Werner!

Best wishes,
Doug


-----Original Message-----
From: bernd.pauli at paulinet.de
To: Meteorite-list at meteoritecentral.com
Sent: Tue, Sep 29, 2009 6:06 am
Subject: [meteorite-list] Red spots on Tatahouines?



Hi Melanie, Jeff, Werner, and List,

BARRAT J.A. et al. (1999) The Tatahouine diogenite: Mineralogical
and chemical effects of sixty-three years of terrestrial residence
(MAPS 34-1, 1999, 091-097, excerpts):

"The crystals of orthopyroxene ... contain many inclusions ... of
silica,
troilite,
chromite, and *metal*. The silica inclusions ... contain silica with
either
metal
(Fe, 98%; Ni + Co, 2%) or chromite."

and:

"The samples collected in 1994 contain secondary minerals, which
clearly
developed
in the soil during their 63 years of terrestrial residence. First, *Fe
stains*
replace metal
or troilite inclusions on the surfaces of the clasts in contact with
soil or
inside fractures.
Second, yellowish to *light orange calcitic aggregates* were found in
some
samples.
They mainly occur as a partial filling with a rosette texture or
completely fill
some
fractures (ca. 100 ?m wide)."

Best wishes,

Bernd


______________________________________________
http://www.meteoritecentral.com
Meteorite-list mailing list
Meteorite-list at meteoritecentral.com
http://six.pairlist.net/mailman/listinfo/meteorite-list
Received on Tue 29 Sep 2009 12:12:35 PM PDT