[meteorite-list] Kalahari 008 and weathering

From: Randy Korotev <korotev_at_meteoritecentral.com>
Date: Thu, 19 Apr 2007 11:29:59 -0500
Message-ID: <200704191629.l3JGTh012685_at_levee.wustl.edu>

Doug:

>"wt.%: Al: 14.68; Si: 20.73; Mg: 2.68; Fe: 3.5; Ca: 11.1."

Those values are all consistent with lunar rocks, but also terrestrial
rocks made of the same minerals - plagioclase, pyroxene, and olivine.

> Thanks for posting the photo and the nice web page Randy. Would you know
> how a weathering grade was assigned (probably there is more to this
> seeing it was classified at Wlotzka's Max Planck) , I wonder how
much iron and FeS
> of the 3.5% Fe was actually available/useful to this end? W1 is
> statistically quite a nice rating to fall off the turnip truck, wouldn't a
> simple Antarctic "A" be more appropriate?

I don't really know "how they did it," but most brecciated lunar
meteorites do contain grains of metal - metal from asteroidal
meteorites that strike the Moon and that created the breccias in the
first place. Some lunar meteorites contain a few percent chondritic
material. Metal grains are there if you look for them (can't miss
them with reflected light microscopy). Most of the sulfur in soils
from the lunar highlands comes from meteorites.

Note also that ordinary chondrites weather differently than achondrites.
When iron rusts, there's a volume expansion, which forces the rock to
crack, accelerating the weathering. There's not enough metal in most
achondrites for that process to happen.

Randy
Received on Thu 19 Apr 2007 12:29:59 PM PDT