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Re: Aquatic Plants Digest V3 #384

Paul Sears wrote, in reply to Dave Gomberg:

> > From: Dave Gomberg <gomberg at wcf_com>
> > Subject: Reducing diet
> >
> > Where there had been laterite below the gravel, there was now a mixture of
> > laterite
> > and COMPLETELY REDUCED IRON.   It looked like tiny iron filings.
> 	What makes you think it was iron metal?  Did it rust in water
> and air?
> >
> > I am pretty sure this black stuff was not a sulphur compound (tho it could
> > have been FeS)
> > because it was very dense.
> 	Magnetite (Fe3O4) is black, magnetic and dense.  There are also
> several iron/sulphur phases that fit those criteria.

I don't think that metallic iron will form in the presence of water under
any condition that exists in the earth's crust.  Magnetite crystallizes
from molten rock and can form from super-heated solutions at depth, but
these aren't much like aquarium conditions.

If it is iron or magnetite, then it came from somewhere else.  It didn't
form in the tank.  Of course, if it did form in the tank then I imagine
some folks over at US Steel might be real interested in the process...

Pyrite (FeS2) can form in the absence of oxygen when the right bacteria
get to work.  Sometimes pyrite formed this way when viewed under high
magnification will have a distinct look like a bunch of grapes -
apparently casts of the bacteria that formed them.  Siderite (FeCO3) can
also precipitate under reduced conditions.

Also, some iron oxyhydroxides minerals when well crystallized are dense
and sometimes black.  Some of that well-crystallized material might have
been mixed with the original laterite.  The time in the tank probably
wouldn't be long enough to allow the amorphous iron hydroxides to
crystallize, but heck, who knows?

Roger Miller