[meteorite-list] Troilite inclusions

[MexicoDoug 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