[meteorite-list] blue chondrule in a CM2

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Sat, 06 Feb 2010 19:11:29 -0500
Message-ID: <4B6E0531.4010107_at_usgs.gov>

CAIs can be quite round. The famous "Blue Angel" CAI was a fairly
round, mm-size object in another CM chondrite, Murchison (this
publication was in 1982-ish in GCA). Not all hibonite in meteoritic
CAIs is the same color. The blue comes from Ti3+, formed under reducing
conditions. The blue ones are very well-known in CM chondrites, but
hibonite goes all the way from blue to white depending on the conditions
of formation and maybe bulk composition.

To tell if it's really a CAI, you'd probably have to analyze some grains
or make a polished section.

If this is a hibonite-bearing CAI, is it important? There is current
research on hibonite in CMs, e.g.
http://linkinghub.elsevier.com/retrieve/pii/S0016703709003251. I would
contact somebody like Andy Davis at U. Chicago, a coauthor on this
paper, and get his opinion if you're thinking of donating this to science.

Jeff

On 2010-02-06 5:20 PM, Zelimir.Gabelica at uha.fr wrote:
> Hello Jeff, Matthias, Ted, all,
>
> Your wise suggestions about the blue inclusion are highly appreciated.
>
> I also first thought of hibonite that was mentioned in a similar
> discussion we had on the list a couple of years ago. At the time, Jeff
> Kuyken showed us a chondrule-like inclusion in Isheyevo and hibonite
> was one of the hypotheses retained . I don't really remember the
> detailed discussion that resulted but this info is now probably hidden
> somewhere in the archives .
> By luck, this debate (with hibonite hypothesis) as well as the
> inclusion pics are still available on Jeff's site (Jeff K, I hope you
> don't mind if I provide the link):
>
> http://www.meteorites.com.au/features/isheyevo.html
>
> The blue color in Isheyevo (as it is in Allende shown by Ted), is more
> intense than the light blue shade of our TNZ "chondrule" so I did not
> retain at first that hypotheis. (also because all the terrestrial
> hibonites I have seen are dark brown but more often just black; the
> best crystals so far come from Madagascar and I have in my mineral
> collection a 6x4x3 cm single cristal, just full black- from the famous
> Betroka deposit).
>
> I now realize the hibonite hypothesis is very likely.
> But enstatite is another possibility indeed. I have a terrestrial
> enstatite sample that is blue-green. The synthetic enstatites we once
> had synthesized in the lab are logically white.
>
> Two last questions (sorry for insisting):
>
> 1) Should we consider this just as a curiosity or does someone believe
> this could have some pertinent significance in the case of a CM2
> chondrite ?
>
> 2) How can we make sure the "round light blue circle" shown here is a
> chondrule or a CAI ? Jeff firmly states that the TNZ hibonite is
> embedded in a CAI and Ted shows the same in Allende. Would that imply
> the TNZ "circle" is also a CAI rather than a chondrule, despite of its
> quasi perferctly round shape ?
>
> My best wishes,
>
> Zelimir
>
>
>
> Ted Bunch <tbear1 at cableone.net> a ??crit? :
>
>> Dear Zelimir- Jeff beat me on the response.
>>
>> Attached is a true hibonite in an Allende CAI. Your blue object could
>> be a
>> lighter blue hibonite or an enstatite chondrule that, on occasion, has a
>> blue hue depending on the light source, angle of illumination, light
>> scattering, etc.
>>
>> Ted
>>
>>
>> On 2/6/10 10:06 AM, "Zelimir.Gabelica at uha.fr" <Zelimir.Gabelica at uha.fr>
>> wrote:
>>
>>>
>>> Hi List,
>>>
>>> Here are 3 pics of a genuine blue chondrule spotted upon breaking a
>>> fagment of the CM2 meteorite Tanezrouft 082 (purchased last June in
>>> Ensisheim, from A. Gouesslain/J.-L. Parodi, the meteorite finders).
>>>
>>> See here:
>>>
>>> http://www.agab.be/question/question.html
>>>
>>> Question: what could be the origin of such a strange turquois-like
>>> blue color ?
>>>
>>> Could it be due to some traces of Cu2+ salts neutralizing some
>>> refractory silicates ? (despite tha fact that the presence of Cu was
>>> apparently not reported in the meteorite analysis, see the Met. Bull.
>>> writeup added in the URL).
>>>
>>> Or could that just be (sometimes) the natural color of some
>>> (ortho)pyroxenes ?
>>>
>>> Or olivine ?
>>> However, I don't remember having ever seen any olivine showing such a
>>> "true" blue color. Shouldn't olivine (always?) rather be
>>> "olive-green", whatever its origin (terrestrial or asteroidal) ?
>>>
>>> Thanks for sharing your thoughts or expertise.
>>>
>>> My best,
>>>
>>> Zelimir
>>>
>>>
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>>
>
>
>
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-- 
Dr. Jeffrey N. Grossman       phone: (703) 648-6184
US Geological Survey          fax:   (703) 648-6383
954 National Center
Reston, VA 20192, USA

Received on Sat 06 Feb 2010 07:11:29 PM PST