[meteorite-list] Bull's-eye chondrule assumptions (& New Meteorite Atlas)

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Wed May 4 08:58:43 2005
Message-ID: <5.1.0.14.2.20050504085623.029e5418_at_gsvaresm02.er.usgs.gov>

No, just dissolution of glass (and partial replacement by clay minerals).

At 08:50 AM 5/4/2005, Gerald Flaherty wrote:
>Hi Jeff and List,
>Jeff you use the term bleaching, is that an oxidation process?
>Jerry Flaherty
>----- Original Message ----- From: "Jeff Grossman" <jgrossman_at_usgs.gov>
>To: <Meteorite-list_at_meteoritecentral.com>
>Sent: Wednesday, May 04, 2005 8:30 AM
>Subject: Re: [meteorite-list] Bull's-eye chondrule assumptions (& New
>Meteorite Atlas)
>
>
>>Oh, I didn't see the other question in this thread. The "bites" out of
>>"pac-man" chondrules can have one of two origins. The most popular
>>explanation is that the chondrule underwent a low-velocity collision with
>>another chondrule during the time in its cooling history when it was
>>mostly crystallized but still warm and plastic. However, a much better
>>explanation for some of these, including the ones in some of your photos
>>I think, is that the chondrule originally contained a significant amount
>>of Fe-Ni metal and/or FeS. This formed a round bead when the chondrule
>>was cooling and migrated to the surface due to centrifugal force as the
>>chondrule was spinning. At some point after the chondrule solidified,
>>the metal/sulfide bead was lost. There is a picture of a chondrule that
>>still has the metal bead in place in a paper I wrote 20 years back
>>(Grossman & Wasson 1985, GCA 49, 925-939, The origin and history of the
>>metal and sulfide components of chondrules).
>>
>>Whichever reason for the "crater" is correct, bleaching occurred on the
>>parent asteroid, following the contours of the crater.
>>
>>Jeff
>>
>>At 03:32 AM 5/4/2005, Jeff Kuyken wrote:
>>>I was just going through my emails and found this one. Well, I have just
>>>received Marvin Killgore's new "A Color Atlas of Meteorites in Thin Section"
>>>from Mike Jensen. I highly recommend this book which has numerous fantastic
>>>images of MANY different meteorite types.
>>>
>>>One of the things I noticed was that a few of the meteorites presented
>>>actually have Bull's-eye chondrules. For those of you who may have purchased
>>>this book, the page references I have found so far include:
>>>
>>>NWA 487 (L/LL3.2) P20-23
>>>LEW 86018 (L3.1) P44-47
>>>ALH 77176 (L3.2) P48-51 (Remnant/Damaged)
>>>QUE 97008 (L3.4) 56-57
>>>LEW 87284 (L3.6) P64-67
>>>ALH 85033 (L4) P72-73
>>>GOLD BASIN (L4) P76-79 (Remnant/Weathered)
>>>MOUNT TAZERAIT (L5) P80-81
>>>
>>>Any thoughts?
>>>
>>>Jeff
>>>
>>>
>>>----- Original Message -----
>>>From: bernd.pauli_at_paulinet.de
>>>To: Meteorite-list_at_meteoritecentral.com
>>>Sent: Thursday, March 17, 2005 7:48 AM
>>>Subject: [meteorite-list] Bull's-eye chondrule assumptions
>>>
>>>
>>>John and Dawn wrote:
>>>
>>> > We seem to have several of them in our new LL3
>>>
>>>Christian responded and presented some stunning pictures:
>>>
>>> > I have many of them: ...
>>>
>>>Whereupon John and Dawn wrote:
>>>
>>> > I really liked NWA 1770
>>>
>>>I am in love with the perfect bull's eye in Christian's NWA 724!
>>>
>>> > www.austromet.com/collection/NWA_0724_5.646g.jpg
>>>
>>>Do I have any ideas on the formation of such chondrules?
>>>
>>>Only some ideas, no references, no direct links: These chondrules
>>>obviously occur only in unequilibrated chondrites of types H3.x,
>>>L3.x, and LL3.x (by inference probably also in some E3 chondrites),
>>>up to petrologic type 4.
>>>
>>>Darker core material seems to be enveloped by a lighter-colored, in
>>>some cases almost concentric ring of (fine-grained, dusty?) material.
>>>
>>>The process that gave birth to such chondrules may have been either
>>>accretionary or condensational and the environment may have been
>>>dusty (which would point to early solar system processes).
>>>
>>>Obviously only a limited number of chondrules underwent this process
>>>so that the bull's-eye chondrule formation may have been a selective
>>>process (time, distance from the protosun, dusty environment..I don't
>>>know).
>>>
>>>It would be interesting and helpful if someone detected such bull's-eye
>>>chondrules in one of their thin sections so that we could draw further
>>>conclusions on their mineralic compositions (core material, rim or seam
>>>(?) material, high-temperature, low-temperature phases, etc.).
>>>
>>>Esteemed list member Jeff Grossman wrote several papers on chondrule
>>>formation, chondrule composition, zoned chondrules, etc. Maybe he can
>>>enlighten us on these "Eyes of Taurus", the Bull, my Constellation :-)
>>>
>>>Best wishes,
>>>
>>>Bernd
>>>
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>>>
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>>
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Received on Wed 04 May 2005 08:58:40 AM PDT