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

From: MexicoDoug <MexicoDoug_at_meteoritecentral.com>
Date: Sun, 15 Apr 2007 10:53:23 -0500
Message-ID: <006001c77f76$37d4a620$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?"

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
Received on Sun 15 Apr 2007 11:53:23 AM PDT