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

From: MexicoDoug <MexicoDoug_at_meteoritecentral.com>
Date: Mon, 16 Apr 2007 02:00:21 -0500
Message-ID: <008c01c77ff5$12349720$d1068cc9_at_0019110394>

"Doug, List What else occurring in meteorites can be crystal clear like
some
quartz? Is it magnesium? I'm referring to something grainy like
beach sand. Mike"

Hi Mike, List,

Good question as the waters get muddied on this quartz "rule" for
meteorites.

How about Plagioclase feldspars - which are 'tectosilicates'
("molten(glassy) silicates")?

Then, the silicates: pyroxenes (e.g., orthopyroxenes) can be transparent
looking especially when thin.

It's hard to tell if something is really 'clear' when it is in the matrix of
grainy stone of varying shades and tones - don't you think? About the best
I can do visually is say it looks a little transparent. That is a minor,
but important distinction. I think conchoidally fractured oligoclase for
example could give this impression. The way the fracture reflects the light
to your eyes can also give the glassy impression - as glass, quartz have
conchoidal fractures.

In summary, you're right; all that glitters is not quartz, there are plenty
of silicate grains to worry about, many which are hard to tell apart by
inspection.

Good question and time to look at the meteorites again with this in mind...

Best wishes and Great Health,
Doug

----- Original Message -----
From: "Michael Murray" <mmurray at montrose.net>
To: "MexicoDoug" <MexicoDoug at aim.com>
Sent: Sunday, April 15, 2007 7:24 PM
Subject: Re: [meteorite-list] Two quartz questions-- one on topic, one off.


> Doug, List
> What else occurring in meteorites can be crystal clear like some
> quartz? Is it magnesium? I'm referring to something grainy like
> beach sand.
>
> Mike
>
> Mike
>
>
> On Apr 15, 2007, at 10:57 AM, MexicoDoug wrote:
>
> > "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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> >>
> >
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>
Received on Mon 16 Apr 2007 03:00:21 AM PDT