[meteorite-list] Re: Questions - meteoritics

From: Steven Singletary <jumper_at_meteoritecentral.com>
Date: Thu Apr 22 09:41:12 2004
Message-ID: <200102241425.JAA10102_at_melbourne-city-street.MIT.EDU>

>
>same page: I assume oxygen fugacity has to do with oxygen dissapearing or
>leaving for some reason from the parent bodies, but I really don't
>understand what process they are referring to. Could someone explain? The
>properties are given in terms of FMQ and IW... What are these? > QFM =
>quartz-fayalite-magnetite oxygen buffer
>


IW is iron wustite. It and QFM are standards by which we measure oxygen
fugacity, in other words how much oxygen is available to react. If you are
in an oxidizing environment (high fO2) iron will be oxidzed. This is more
commonly known to us earthbound beings as rusting. If you are at low fO2,
such as below iron-wustite, you are at reducing conditions and no oxygen is
available to react, so you'll commonly find iron in it's pure metallic
state, assuming of course we're talking about a magmatic process where
there's lots of iron. So if you hear someone say "the process is occuring
below QFM, the fO2 of the system is below the fO2 where
quartz-fayalite-magnetite are in equilibrium at a given T and P.


Hope that helps.
If anybody else can clear that up or add anything please feel free.


Steven Singletary
54-1224
Dept. Earth, Atmospheric, and Planetary Sciences
M.I.T.
Cambridge, Ma., 02139
Jumper_at_MIT.EDU

Blue Skies!!
Received on Sat 24 Feb 2001 09:28:23 AM PST