[meteorite-list] photo link - a cosmic marble

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Sun Nov 13 14:55:14 2005
Message-ID: <DIIE.0000003200003FA4_at_paulinet.de>

Hi Stefan and List,

My NWA 2384 (LL4) from the Hup?s has a similar-looking megachondrule, only
difference is it doesn't have these alternating rings of olivine and pyroxene
mentioned below. Here's my description: "Large oval yellowish-white pyroxene
chondrule measuring 18.5 x 8.5 mm with concentric arcs outlined by finely
dispersed opaque material and a coarser-grained core."

I had the pleasure of viewing several other photos that Stefan took of this L-breccia,
and, for heaven's sake, what a meteorite, what a wonderful, multilayered chondrule,
and then all those exotic and mind-blowing clasts (some of which are almost certainly
primitive and carbonaceous) and inclusions (one large, pale yellow-white aggregate
may be L6, LL6, or even achondritic).

Mike Farmer wrote:

"WOW, that is so cool! How large is it?"

It is approximately 13 mm in longest dimension

Matt wrote:

"That looks like an "accretionaty lapilli"...very cool!"

Right on target, I think.

http://www.meteoriten.com/L-breccia-large-chondrule.jpg

HUTCHISON R. (2004) Meteorites: A Petrologic, Chemical, and Isotopic
Synthesis (Cambridge Planetary Science Series, pp. 506, p. 223):

Rims could have formed on chondrules and clasts by the sintering of dust layers.
This is analogous to the formation of accretionary lapili in pyroclastic rocks
on Earth.

Such concentrically layered chondrules are also to be found in CR2 chondrites,
and, according to Weisberg et al., rim materials accreted onto solidified cores
and were then (partially) melted. The authors also state that in El Djouf 001
the larger, multilayered chondrules (some of them > 4 mm) consist of alternating,
concentric layers of olivine and/or pyroxene + FeNi metal surrounding a core of
coarser grained olivine and/or pyroxene + FeNi metal. Some El Djouf chondrules
have an outer layer of fine grained, clastic, matrix-like material that accreted
onto it prior to chondrite aggregation.

Stefan's macrochondrule looks almost exactly like this!

WEISBERG M.K. (2001) Sahara 00182: The first CR3 chondrite and
formation of multi-layered chondrules (MAPS 36-9, 2001, A222):

"Many chondrules are concentrically layered aggregates containing cores of one or
more crystals of forsterite and/or metal surrounded by mantles of metal blebs, followed
by silicate shells consisting of olivine and/or pyroxene. Some layered chondrules have
barred olivitic or cryptocrystalline cores surrounded by mantles of metal blebs, followed
by coarser olivine- or pyroxene-rich shells. In some cases, the layered chondrules have
rims of silica-rich material similar to those described on layered chondrules in some CR
chondrites."

and furthermore:

"The multi-layered chondrules may represent an early generation of chondrules that record
multiple episodes of accretion and heating in the nebula. The cores of the layered chondrules
range from aggregates of materials that experienced low levels of partial melting to barred
or cryptocrystalline textured materials that may have been completely molten."


References:

M.K. Weisberg et al.(1992) Formation of layered chondrules in CR2 chondrites:
A petrologic and oxygen isotopic study (abs. in Meteoritics 27-3, p. 306).

M.K. Weisberg et al.(1991) El Djouf 001: A new CR2 chondrite
(Meteoritics 26-4, 1991, 406-407).
Received on Sun 13 Nov 2005 02:55:07 PM PST