[meteorite-list] Chondrule size range?

From: bernd.pauli_at_paulinet.de <bernd.pauli_at_meteoritecentral.com>
Date: Tue May 24 13:17:23 2005
Message-ID: <DIIE.000000380000387C_at_paulinet.de>

Tom wrote:

> This meteorite was packed with chondrules but one chondrule stood out,
> nothing special as far as chondrules go, but it is huge, not huge for
> a chondrule, but huge for this meteorite! I am wondering how one big
> chondrule could end up in a meteorite. I have seen pics of other meteo-
> rites with one large chondrule, but never heard an explanation of why.
> Or maybe the question should be, why are the others so small?

> http://img.photobucket.com/albums/v609/peregrineflier/DSCN1287.jpg
> http://img.photobucket.com/albums/v609/peregrineflier/DSCN1293.jpg


Hello Tom and List,

It *is* large, almost 5 mm in diameter, and thus almost a *macrochondrule*
according to the definition as given by J.C. Bridges and R. Hutchison in
their article:

BRIDGES J.C. et al. (1997) A survey of clasts and large chondrules
in ordinary chondrites (Meteoritics 32-3, 1997, pp. 389-394).

> Or maybe the question should be, why are the others so small?

No, the large ones are the exception to the rule! The above authors state:

- Macrochondrules occupy only about 1% (!) of meteorite surfaces

- Macrochondrules or clasts were found in about 4% of the 833 ordinary
  chondrites examined

- Evidence for limited chondrule size ranges has been obtained by measuring
  a set of 62 chondrules spearated from LL chondrites. Using the data set
  suggests that > 99% of chondrules in those meteorites have diameters smaller
  or equal to 4.1 mm.

- The H chondrites, as expected, contain a smaller proportion of large objects
  than the L and LL chondrites (in other words, H chondrites, on the average
  have smaller chondrules than L or LL chondrites)

> [I've] never heard an explanation of why.

Oh boy, I hoped you wouldn't ask that question :-)

..nope ... :-(

The famous meteoriticist M.K. Weisberg wrote in an abstract:

"Macrochondrules may have formed in nebular regions:

- with greater dust densities
- differing dust/gas ratios
- and/or: higher electrostatic attraction between particles, ...

and he also wrote:

"macrochondrules may be the result of impact spraying."

WEISBERG M.K. et al. (1988) Macrochondrules in ordinary
chondrites: Constraints on chondrule-forming processes
(Meteoritics 23-3, 1988, A309-310).

and, a drum roll, please, for the Gunlock, L3.4 chondrite (some say it's an L3.2):

It contains a golfball-sized chondrule which must originally have measured
about five centimeters (!) in diameter. Unfortunately, most of it is missing :-(
but meteoriticists were able to reconstruct it :-)


Best wishes,

Bernd

P.S.: According to David Weir, a 48-mm ellipsoidal
chondrule was found in Djati-Pengilon, an H6 chondrite.
Received on Tue 24 May 2005 01:17:21 PM PDT