[meteorite-list] Red spots on Tatahouines?

[Mexicodoug]

Oops one typo:

"The "rosette" color Bernd cites"

should have been:

The "orange" color Bernd cites.

They were referring to a rosette pattern, not color ... for example, 
see:

CARBONATES IN THE MARTIAN ORTHOPYROXENITE ALH 84001: EVIDENCE OF 
FORMATION DURING IMPACT-DRIVEN METASOMATISM. R. P. Harvey and H. Y. 
McSween, Jr., Lunar and Planetary Science XXVI, pp. 555-556, LPI, 
Houston, TX, 1995.

Kindest wishes
Doug


-----Original Message-----
From: Mexicodoug <mexicodoug at aim.com>
To: bernd.pauli at paulinet.de; Meteorite-list at meteoritecentral.com
Sent: Tue, Sep 29, 2009 12:12 pm
Subject: Re: [meteorite-list] Red spots on Tatahouines?


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 h
ematite 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 µm 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 Tatahouine20diogenite: 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 µm wide)." 
 
Best wishes, 
 
Bernd 
 
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