[meteorite-list] Troilite inclusions

From: MexicoDoug_at_aol.com <MexicoDoug_at_meteoritecentral.com>
Date: Wed Jan 5 01:13:14 2005
Message-ID: <e6.6085d452.2f0cdf74_at_aol.com>

En un mensaje con fecha 01/04/2005 11:13:38 AM Mexico Standard Time,
Z.Gabelica_at_uha.fr escribe:
Conversely, in space (absence of oxygen and, hence, less (or no)
possibilities for Fe2+ to get oxidized to Fe3+ ), the system both has TIME
and CONDITIONS to stabilize all the Fe as Fe(2+) perfectly compensating
the S(2-) anions in the structure and thereby generate troilite instead of
pyrrhotite.

Zelimir

Zelimir,

Speaking of S(-2) anions really sounds odd to me because I sort of doubt
that sulfur is floating around in such an unstable state (with possible
exception to a primative solar wind?) in the solid or gaseous phase but I guess you
never know with these supernovas. More likely I would expect it to be
something more typical like S8 solid structure and neutral. As to your thoughts
that there is plenty of time for an equilibration process to stabilize all the
Fe(II) ferrous ion, that is really counterintuitive to me, considering the
iron seems to be neutral throughout the rest of the core which is why we get
meteorites with metal and not rusty cores to start with. It is much more
believable to me that we start out with the elements and then they react at the
high temperatures in the foundry planetesimal core. Thus the troilite very
plausibly would be produced right then and there in a 1:1 Fe-S ratio without
looking for a more complicated explanation. If any complication to that first
attempt at a model is to be made regarding the 1:1 "charge balance" I would
much rather stick to my original thoughts in that the FeS, if you look at the
paper I quoted with the phase diagram has plenty of opportunity to be miscible
with the elemental iron or alloy. Any excess sulfur not with an iron partner
in that labile phase would most likely not be wanted at the party and
precipitate out or go away somewhere else with another partner or phase. The point
being that the environment is saturated with iron-not the other way around
like occurs on Earth-, so why be surprised that the FeS compound that results
is also saturated with iron:) The type of material that is the precursor of
FeS may not be strictly ionic, whether elemental or compounds, though in
space conditions I suppose anything is possibly present or not.

Even odder sounding is is that you say there is less (or no) opportunity in
space for oxidation of ferrous ions. I don't have any direct experience in
studying that, but the "absense of oxygen" sounds like you are terraforming
the universe. Of course in "space" there are plenty of opportunities for
oxidation, which I would keep in mind from my old Chem professor is "loss of an
electron"; oxygen of course is just one of many electron acceptors chemically
speaking. But more importantly, the list members in Scandanavia, Russia, and
Alaska, etc., probably can tell us around this time of year that the solar
wind, for example does a great job of juggling and stripping electrons around
in space - just look at the Aurora Borealis (caused by perhaps not
coincidentally to this question at hand - the Earth's own molten iron core - very
suggestive to me)! Summarizing, there is more than one way to skin a cat and Earth
is just one quite interesting place of many...

Saludos, Doug
Received on Wed 05 Jan 2005 01:13:08 AM PST