Why does quartzite glow?
Eric Buddington
In article <345BD8...@sprintmail.com>, Ann Welch wrote:
>I'm not sure if this is the correct place to find out about this
It is.
>Why does quartzite glow when you rub two pieces together? If you
>haven't tried it, a very dark room is required.
I believe this is because quartz is piezoelectric, which means that
the crystals generate a voltage difference across themselves when
deformed (conversely, they'll deform if you put an electric voltage
across them - I think these two phenomena together are used to keep
time in a quartz watch.)
When you rub the rocks together, some points generate enough voltage
to spark, creating the glow.
Can anyone explain better how a quartz watch works? Is the resonance
of a quartz timing circuit proportional to the size of the crystal?
Or does the higher voltage created by a larger crystal negate the
effects of the larger size?
Eric
Rusty Divine
Ann,
My only training on the subject was a course I just completed on
mineralogy.
The optical effect of triboluminescence, where a meaterial becomes luminous
when scratched, rubbed, or crushed, sounds like what you are refering too.
But I didn't know quartz acted this way, I know fluorite and sphalerite do,
however. Fluorite resembles quartz in some ways too, are you sure it's
quartz you have?
Ann Welch wrote:
> I'm not sure if this is the correct place to find out about this, but I
> thought I would give it a try.
>
> Why does quartzite glow when you rub two pieces together? If you
> haven't tried it, a very dark room is required.
>
> Thanks,
> ann
Jo Schaper
Rusty Divine <Div...@ix.netcom.com> wrote:
>Ann Welch wrote:
I don't think triboluminescence is quite as intense as the
piezoelectricity of quartz. For any of you cave people out there,
striking two pieces of flint (cryptocrystalline quartz) or flint on
steel, can actually cause fire if the sparks are correctly directed
onto tinder. Ever wonder why strikers in lighters are called
"flints"? There is a reason. Two pieces of flint, when struck, not
only make a spark, they also give off an acrid burning odor.
If you want a tasty demonstration of triboluminescence, take a good
friend into a dark room (or yourself with a mirror) and chew
wintergreen mints (must be sugar--not sugar free) and watch your mouth
as you chew.
P.S. It is very easy to tell fluorite from quartz--fluorite is
scratched by a steel knife, quartz scratches the knife. Also, Fluorite
has a "flashy" clevage look and cleaves/crystallizes in the
cubical/octohedronal crystal family, Quartz has a conchoidal
(literally shell-like irregular like broken glass) fracture, does not
cleave, and most commonly forms hexagonal crystals. In fact, except
that both can be transparent to translucent and multicolored, and are
fairly common, I can't think of any other similarities.
Jo Schaper
scha...@mail.idt.net
Sanman
Eric Buddington wrote:
>
> In article <63m1uv$o...@nnrp2.farm.idt.net>, Jo Schaper wrote:
>
> > Quartz has a conchoidal (literally shell-like irregular like broken
> > glass) fracture, does not cleave, and most commonly forms hexagonal
> > crystals.
>
> crystal structure. I'm used to thinking of conchoidal fractures coming
> from poorly-crystalized substances (most obviously obsidian, and
> similarly commercial glass).
>
> Is there a good reason why this is not so? (Yes, I insist that the
> natural world justify itself to me ;))
>
> Eric
The conchoidal fracture of quartz is explained by quartz's
crystalline structure. It has a corkscrew like structure.
The corkscrews ruin any chance for cleavage which requires
a plane of weakness. When a fracture occurs it hits the
corkscrews and is diverted either up or down. Continual
fracturing results in a tighter and tighter curve either
upward or downward and produces the shell-like (concave,
curved fracture).
Conchoidal fracture is not an indicator of poorly-crystal
lized substances as there are many well crystallized
substances have conchoidal fracture (even substances that
have good cleavage). You are correct in that many poorly
crystallized substances have conchoidal fracture such as
glass, obsidian, amber, jet and metamictic minerals, but
don't apply that similarity to all substances with conchoidal
fracture.
--
David Sanborn
San...@digex.net
http://mineral.galleries.com
Eric Buddington
Jo Schaper
beebe...@aol.com (BeeBeeBarr) wrote:
>Of course, another reason the cleavage is not often observed is that almost
> everyone KNOWS quartz has no cleavage, just the classic conchoidal fracture.
> To quote a couple of great natural philosophers:
>-- Bill Baker Barr (not named after the street)
>Ann Arbor, Michigan
Remember too, that quartz has both crytalline and cryptocrystalline
varieties. After 35 years of breaking rocks, (much of it quartz
geodes or poor grade chalcedony or chert) I have seen crystalline
quartz break along crystal faces into separate crystal fragments, but
I have never seen either individual crystals break with anything but a
glassy conchoidal scallop (for the pure stuff) or an irregular
fracture for quartz with impurities. The cryptocrystalline stuff
always breaks along cracks or natural flaws in the rocks, or else you
can pound it for hours until one develops, but chipping away flakes in
the process. If the rock breaks at an angle away from but
incorporating a flaw, the break may go this way and that, again,
following the intergrown crystal faces if they are large enough, if
not, it chips in semi circles. This chipping property of flint or
chert is what made is so wondeful for Amerindian artifacts.
Sorry, no one is going to make me believe quartz has
rhombohedronal cleavage; I've also broken enough calcite to know what
rhombs are when they happen. Never happened on any of my quartz.
My quote: "Seeing's believing."
Jo Schaper
scha...@mail.idt.net