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

From: Jeff Grossman <jgrossman_at_meteoritecentral.com>
Date: Wed May 4 08:19:11 2005
Message-ID: <5.1.0.14.2.20050504080711.029a9b30_at_gsvaresm02.er.usgs.gov>

If the chondrule you mean is the black one with the light colored rim at
the left side halfway up, this looks to be a bleached chondrule. See:
http://articles.adsabs.harvard.edu/cgi-bin/nph-iarticle_query?2000M%26PS...35..467G

Such chondrules start out as very fine-grained radial pyroxene chondrules
or cryptocrystalline chondrules, both of which are composed of very tiny,
densely packed pyroxene grains embedded in glass. Apparently, all ordinary
chondrites experienced at least a small amount of aqueous alteration as
fluids moved through the parent asteroid. Water dissolved the glass at the
edges of these chondrules, leaving a rather porous network of pyroxene
crystals behind. This causes the "bleached" effect you observe when the
chondrule is sliced open and polished. You find these up to petrologic
type 4, but I've seen them even in a few type 6 ordinary chondrites.

If you mean a different chondrule, let me know.

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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Received on Wed 04 May 2005 08:16:49 AM PDT