iandol on sat 5 may 01
Given that Kaolin is formed from Granite rocks by various processes, to =3D
what extent will minerals other than Quartz, Feldspars and Micas =3D
influence the properties and behaviour of the clay when it is used in =3D
glazes as well as in a plastic body?
For example, Tourmaline is a common accessory mineral in granite or =3D
granite like rocks. This substance contains Boron. So it might be =3D
inferred that clays which are derived from source rocks which contained =3D
this mineral might have beneficial self fluxing properties at higher =3D
firing temperatures. This supposition is based on the mineral surviving =3D
the weathering processes.
Just don't ask what brought this into my mind.
Best regards,
Ivor Lewis. Redhill, South Australia
Logan Oplinger on mon 7 may 01
Hi Ivor,
I cannot say for certain what residual minerals/ elements may be expressed as a result of the weathering process of tourmaline, but since kaolin and quartz are among the most refractory w/ respect to weathering, I would suspect that any remaining boron minerals would also have to be similarly refractory to the weathering process. If I remember my basic geology correctly, granite weathering to clay is an insitue process that results in all elements forming more soluble minerals being leached away. I will have to see what I can find on the weathering of pegmatites.
Would it be possible for boron to be contained within the kaolin molecule as a replacement ion, or as an ion bridging between the layered kaolin molecules?
I am sure someone else will have a good answer here.
Logan Oplinger
---- you wrote:
> Given that Kaolin is formed from Granite rocks by various processes, to what extent will minerals other than Quartz, Feldspars and Micas influence the properties and behaviour of the clay when it is used in glazes as well as in a plastic body?
> For example, Tourmaline is a common accessory mineral in granite or granite like rocks. This substance contains Boron. So it might be inferred that clays which are derived from source rocks which contained this mineral might have beneficial self fluxing properties at higher firing temperatures. This supposition is based on the mineral surviving the weathering processes.
> Just don't ask what brought this into my mind.
> Best regards,
> Ivor Lewis. Redhill, South Australia
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Joseph Herbert on mon 7 may 01
Ivor Lewis wrote about residual minerals in Kaolin. While quartz could
certainly be present in a primary deposit altered from granite, you would
expect the accessory minerals to also be altered, perhaps to extinction. In
a secondary deposit, one that was transported to its current site, there
should be almost no accessory minerals from the primary source but perhaps
some additional clay minerals from somewhere else. In any event, the potter
is looking at a processed material that has been air floated (small
particles travel farther on an air current, leaving any large heavy ones
behind) assuring the absence of anything other than clay. People how are
mining their own kaolin would need to examine the results of screening and
settling to decide if accessory minerals are a problem.
Joseph Herbert
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