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

From: Rob McCafferty <rob_mccafferty_at_meteoritecentral.com>
Date: Sun, 15 Apr 2007 13:15:50 -0700 (PDT)
Message-ID: <960591.55572.qm_at_web50909.mail.re2.yahoo.com>

Adapted slightly from

http://socrates.berkeley.edu/~eps2/wisc/Lect13.html

Quartz is a very common mineral in most igneous,
metamorphic, and sedimentary rocks. It has also been
found in some lunar rocks and meteorites. It has to be
said that it is only a very minor constituent of these
rocks. An exception rather than a rule.

Quartz forms in rocks of igneous origin (melts) only
after other silicates have incorporated most other
available cations. (such as potassium or magnesium)

Rocks that are more than about 47 percent (by weight)
silicon dioxide contain quartz. The quartz content
increases as the weight percentage SiO2 increases.
 
Quartz can be dissolved in hot water or steam and is
thus transported from place to place in the Earth,
being deposited by cooling of the transporting fluid
or by release of pressure. This is why veins and vast
deposits of quartz can be found.
 
Because quartz is relatively resistant to mechanical
abrasion, it is abundant in stream sediments, on
beaches, and in wind-blown sands. Quartzite and
sandstone are mostly quartz because this is the most
abundant mineral that survives processes occurring at
the Earth's surface. This is not the case with
meteorites.

Cheers
Rob McC


--- Darren Garrison <cynapse at charter.net> 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?
>
> 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 04:15:50 PM PDT