[Rockhounds] Volcanos, earthquakes and things

[Earl R. Verbeek]

Hi Jim,
 
No, I don't thing you're missing anything -- what you wrote sounds
logical to me on all counts.  Yes, the quartz crystals should be
antiparallel, and yes, although quartz commonly exhibits strongly
preferred c-axis orientations in a variety of rocks, I doubt that's true
for the a-axes.  I wish I still had my memory so I could check on
that....
 
        Cheers-   Earl
 
 
-----Original Message-----
From: rockhounds-bounces at lists.drizzle.com
[mailto:rockhounds-bounces at lists.drizzle.com] On Behalf Of Jim
Murowchick
Sent: Tuesday, January 08, 2008 3:19 PM
To: Rockhounds at drizzle.com: A mailing list for rock and gem collectors
Subject: Re: [Rockhounds] Volcanos, earthquakes and things
 
Hi Axel, Pete, and everyone--
    I was just wondering--a prismatic piezoelectric crystal will
generate a
positive charge at one end and a negative charge at the other when
stressed.
Even if the crystals are aligned, wouldn't there be about equal numbers
of
crystals in orientations 180 degrees from each other (antiparallel)?  If
so,
then the charges on the crystals should effectively cancel each other
out in
the rock.
    Also, for quartz, I seem to remember that the piezoelectric effect
is
strongest along the a axes.  If so, then even with aligned prismatic
crystals, there would be an infinite number of possible orientations of
the
a axes (rotated around the c-axis direction).  Again, any electric
fields
produced by compaction would cancel out in the rock.  Does that make
sense,
or am I missing something?  Good mental exercise.
Jim Murowchick
 
 


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