Ron Collins on sun 8 apr 01
Could someone please tell me what phyrophyllite looks like in the raw =
unground state? I think I located a source of this material, but I =
don't know any way of identifying the material. It is fairly soft, can =
be ground with a corn grinder, and is green...any information would be =
appreciated..Melinda in Guatemala=20
Michael Banks on mon 9 apr 01
Hi Melinda,
Pyrophyllite is a relatively rare mineral which is almost indistinguishable
from white mica in field appearance. It often occurs in radiating masses of
platy, pearly, flexible fibres or plates. Semi-transparent, greasy and
usually in light shades of off-white, greyish green, yellowish-blue,
brownish green or completely colourless. It is similar to talc but usually
much more crystalline. In the field it is distinguished by geologists from
talc and muscovite (and other white micas) by its' association (the
associated minerals and rock types). Pyrophyllite generally occurs in two
main associations:
1. Aluminous schists and
2. Masses and veins in severely-hydrothermally altered rocks.
In association (1). it often occurs with other alumino-silicates such as
andalusite, kyanite or sillimanite.
In association (2) it is accompanied by other secondary minerals resulting
from low pH (acid) alteration of the primary rocktype, including kaolinite
(white clay), alunite, pyrite, diaspore and silicification (flooding of the
rock with fine-grained quartz).
This may be all-too technical for you to handle, so the best thing may be to
take your sample to the nearest university Earth Science department and ask
for an X-ray diffraction analysis (XRD). This test is simple and absolutely
diagnostic and even poor, third-world countries often have these facilities.
Please let us know what your mineral turns out to be.
Michael Banks,
Nelson,
NZ
----- Original Message -----
Melinda in Guatemala wrote:
Could someone please tell me what phyrophyllite looks like in the raw
unground state? I think I located a source of this material, but I don't
know any way of identifying the material. It is fairly soft, can be ground
with a corn grinder, and is green...any information would be appreciated..
Joseph Herbert on mon 9 apr 01
You Wrote: "Could someone please tell me what pyrophyllite looks like in the
raw un-ground state? I think I located a source of this material, but I
don't know any way of identifying the material. It is fairly soft, can be
ground with a corn grinder, and is green. any information would be
appreciated . Melinda in Guatemala"
Pyrophyllite is a mineral name, and Phyllite is a rock name.
Pyrophyllite is a slivery white to pale green mica mineral that has a
molecular formula of: Al2Si4O10 (OH)2. It forms in soft, compact clumps
during low-grade metamorphism of felsic or granitic igneous rocks. It
should have a hardness of three or less, easily scratched with a knife blade
but not quite with a fingernail. Your stuff sounds like this mineral.
Phyllite, the rock, is characterized by the shimmering micaceous luster of
the cleavage planes in the rock. The rock looks similar to slate generally,
but has obviously more mica-like character on the cleavages surfaces. I
have seen a phyllite in Tennessee that has a very distinct bronze sheen and
a scattering of BB sized garnets over the cleavage surfaces. Really pretty.
These rocks are named by their major mineral constituent, like Muscovite
Phyllite or Biotite phyllite or even Pyrophyllite phyllite.
Joseph Herbert
Paulette Carr on fri 23 jan 04
Tig,
Pyrophyllite is a hydrated aluminum silicate, Al2O3 - 4SiO2 - H2O, used to
decrease thermal expansion, shrinkage, cracking and extend the firing range ...
usually in a claybody. I have never used it in a glaze. It is available by
name (phyrophyllite) under the raw materials from several ceramic suppliers.
Just check with your favorite, or your catalogs, or if you have difficulty,
contact me off-line, and I will give you a list of my suppliers. Sounds like
you have an interesting glaze project!
To pose a further question, does anyone know why it would be used in a glaze
(other than as a source of silica and alumina) ... any advantages?
My best,
Paulette Carr
St. Louis, MO
Tig Dupre wrote:
>>I understand pyrophyllite is an alumina silicate, but I cannot find it in
my Hamer's. Is there a commercial name for pyrophyllite? Is there a
substitute or alternate substance?
I have a recipe from "Inside Japanese Ceramics" which calls for pyrophyllite,
and I'd like to try the recipe, as is. Then I'd like to make substitutions,
if necessary, to lower the maturing temperature from ^9 to ^6.
So, what's pyrophyllite, please?<<
logan johnson on sun 25 jan 04
Hi Paulette
In my copy of Chapple's Clay & Glazes book it says Pyrophyllite "is used in glazes
similar to that of Kaolin,but it will reduce crazing and thermal expansion better than kaoiln." That's all I know about it. hope this answers your ?
Have a good one!
Paulette Carr wrote:
Tig,
To pose a further question, does anyone know why it would be used in a glaze
(other than as a source of silica and alumina) ... any advantages?
My best,
Paulette Carr
St. Louis, MO
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Paulette Carr on mon 26 jan 04
Logan,
Good to know! I have now added pyrophyllite to my list of materials to use
when I am trying to lower the COE or reduce crazing. I am always looking for
more options.
Many thanks,
Paulette Carr
St. Louis, MO
Logan Johnson wrote:
In my copy of Chapple's Clay & Glazes book it says Pyrophyllite "is used in
glazes
similar to that of Kaolin,but it will reduce crazing and thermal expansion
better than kaoiln."
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