PEDresel@aol.com on wed 13 mar 96
Bob Burruss Writes:
>Unfortunately, both Joanne Grant and K Stevens got the chemistry of
>spodumene wrong. Spodumene is a lithium aluminum SILICATE, not sulfate,
>with the formula LiAlSi2O6. Therefore, neither the fluorine suggested by
>Stevens or the sulfur dioxide suggested by Grant is the cause of the bubbly
>glaze mix.
> I will offer a suggestion about the cause of the foamy glaze mix.
>Spodumene is mined from pegmatites where it occurs with a variety of other
>minerals like petalite, quartz, and feldspars. During mining the spodumene
>and other minerals are ground and must be separated and purified. The most
>common purification method is floatation in an air/water mix to separate
>the minerals by density. Normally a surfactant (soap) is added to aid the
>separation. I'm guessing that the ceramic grade spodumene may still have
>traces of soap in it and that causes the foaming.>started this thread
(sorry, can't >remember your name) said that the foaming
>went away after calcining the spodumene suggests that the soap was burned
>out.
> As a practicing geochemist/geologist, who just started lurking in
>this list, I will try to help on some of these chemistry/geology/mineralogy
>issues. I make pots, too.
Bob may well be right about the soap, but pegmatites often contain a lot of
fluorine bearing minerals and fluorine could be an impurity either through
poor separation of the spodumene, or as trace impurities within the spodumene
itself.
BTW pegmatites contain some impressinve minerals, many of which are important
to potters and it is well worth a look if you get a chance to see some
workings. I remember a pit in the Black Hills of South Dakota USA with
spodumene crystals up to around 15 feet long! (Yes I'm another
geochemist/geologist potter-wannabe).
Evan Dresel who had to have a good horse put down last week and is feeling
sad.
pedresel@aol.com
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