Jeff Lawrence on wed 30 aug 00
Hello Clayart!
I have two wild materials with too much free silica -- without doctoring,
they both dunt themselves into piles of shards (one is a montmorillonite and
the other a rhyolite). According to Hamer, clays can have from 3% to 50%
free silica. Please hold that datum.
Now nepheline syenite is a silica undersaturated feldspathoid (god I love
geology-speak!) with an alumina:silica ratio of 1:1 while your everyday
feldspar has an alumina:silica ratio of 1:3. Please hold these data as well.
If I add some nepheline syenite, it sucks up that free silica and keeps the
body from dunting. I have found that 10% neph sy stops the cracking but
makes the body thixotropic. I have a bizarre conviction that the above data
should allow me to calculate exactly how much neph sy I need, so that I can
put in the bare minimum.
The riddle has several parts that may need more investigation:
1) how much silica is free in a montmorillonite?
2) how much silica is free in a sericitic rhyolite?
3) how do you get a head count on free silica?
For the life of me, though, I have no idea where to begin. Any suggestions?
(besides 'test, test, test!')
TIA,
Jeff
Jeff Lawrence ph. 505-753-5913
Sun Dagger Design fx. 505-753-8074
18496 US HWY 285/84 jml@sundagger.com
Espanola, NM 87532 www.sundagger.com
Michael Banks on sun 3 sep 00
Hi Jeff,
Some answers:
1) Montmorillonite is a clay mineral and when pure has no free silica.
Impure montmorillonite may be accompanied by the free silica minerals
quartz, cristobalite etc, depending on origin.
2) Rhyolites can contain anywhere from 20 to 50% quartz, more rarely
tridymite, or cristobalite. These are the forms "free silica" occurs as.
3) X-ray diffraction (XRD) analysis gives a good indication of the
concentration of the pure silica minerals in a clay sample, in addition to
identifying the clay mineral(s) present. Don't you have a friend with
access to an XRD?
Cheers,
Michael in NZ
----- Original Message ----
Jeff Lawrence wrote: (snip)
> The riddle has several parts that may need more investigation:
> 1) how much silica is free in a montmorillonite?
> 2) how much silica is free in a sericitic rhyolite?
> 3) how do you get a head count on free silica?
>
> For the life of me, though, I have no idea where to begin. Any
suggestions?
> (besides 'test, test, test!')
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