[meteorite-list] Two quartz questions-- one on topic, one off.

From: MexicoDoug <MexicoDoug_at_meteoritecentral.com>
Date: Sun, 15 Apr 2007 11:57:00 -0500
Message-ID: <00a101c77f7f$17dbbf80$f4c85ec8_at_0019110394>

"First question-- since quartz is so highly common on Earth, why is it so
rare in meteorites? Because the oxygen was lost from the parent bodies,
maybe?"

Forgot to mention, for ordinary chondrites, you'll notice that there is
actually a 50-100% greater ratio of Oxygen (to Silicon), in olivine,
pyroxene, feldspar compared to Quartz.

So the "oxygen was lost" idea, if the conditions were right, would favor
more quartz, not less. Again, the difference I imagine is the excess
presence of other metals (like Mg and Ca) tending to form silicates, and
generally the timing of the temperature and pressures available for the
silicon-compound formation.
Best wishes and Great health,
Doug


----- Original Message -----
From: "MexicoDoug" <MexicoDoug at aim.com>
To: "Meteorite Mailing List" <meteorite-list at meteoritecentral.com>
Sent: Sunday, April 15, 2007 10:53 AM
Subject: Re: [meteorite-list] Two quartz questions-- one on topic, one off.


> "First question-- since quartz is so highly common on Earth, why is it so
> rare in meteorites? Because the oxygen was lost from the parent bodies,
> maybe?"
>
> Hi Listees,
>
> Just a stab, I'd think you need to compare the formation processes and
> ingredients on hand when the silicates and silica formed. The basic meat
of
> silicon containing chemical compounds of meteorites (ordinary chondrites
is
> really the focus) are olivine (Fe+Mg-SiO4), feldspar (Na+Ca-AlSiO4),
> pyroxene (Fe+Mg+Ca-SiO3), and a rare occurrence of [silica (pure SiO2)].
>
> Second observation,
> While Earth had a long time to react, oxidize out, equilibrate and leach
out
> this metals or bring them to stable forms, chondrites apparently initially
> were no where near equilibrated in their parent body and thus these metals
> were present in excess and went on to naturally the corresponding
non-quartz
> silicates since quartz requires SiO2.
>
> Third observation,
> Quartz, forms under temperature, pressure + time. We could check the
> chemistry a lot, but I'd guess that given the excesses of metals and lack
of
> complete mixing plus, the lower pressure in smaller bodies like we can
> assume many of the chondtites are, the pressures and temperatures just
> didn't make the quartz threshold. The Al26 heating mechanism may just not
> have been enough alone without the critical mass and time to fire up the
> glass (quartz) making furnace.
>
> In summary, if you could have taken, say, at least the Magnesium out
(let's
> assume the Fe is there to stay in meteorites),you could have thrown a
wrench
> into the olivine-pyroxene setting process, perhaps worked on more massive
> bodies to give more pressure, and heated them more with available
sources -
> you'd have gotten more quartz. Maybe the heart of the chondrite parent
> bodies has the better chance on temperature and pressure, but I'd think
the
> degree of metamorphism on Earth was far, far greater where quartz is more
of
> a watered down endpoint.
>
> Those are my three centavos of thoughts, anyway.
>
> Best wishes and Great Health,
> Doug
>
>
> ----- Original Message -----
> From: "Darren Garrison" <cynapse at charter.net>
> To: <meteorite-list at meteoritecentral.com>
> Sent: Sunday, April 15, 2007 10:43 AM
> Subject: [meteorite-list] Two quartz questions-- one on topic, one off.
>
>
>
> >
> > Second question-- off-topic, but related and should be answerable by one
> of the
> > more general rockhounds on the list. The native stones in my area
> (upstate
> > South Carlina) are a form of quartz. They are very common (as in, you
> can't
> > stick a shovel in the ground without hitting one) and consist of largish
> (up to
> > around the size of a kernal of corn) irregular crystals that are clear
to
> milky
> > with some red staining (rust?). Okay, from my limited geological
> knowledge, the
> > crystal grain size implies that the rocks cooled slowly below the
surface,
> and
> > from the location I assume that they are chunks of the Appalachians, but
> can
> > someone tell me a proper term for the exact kind of rock I have here?
> >
> > Scan of small (around 3 inches) example:
> >
> > http://webpages.charter.net/garrison6328/tmp/quartz_small.jpg
> >
> > http://webpages.charter.net/garrison6328/tmp/quartz.jpg
>
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Received on Sun 15 Apr 2007 12:57:00 PM PDT