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Alternate Names: Amtal c98, Amtalc, amtal c 98

Description: Phlogopite mica

Oxide Analysis Formula
K2O 0.30% -
MgO 29.50% 0.92
Al2O3 0.30% -
Fe2O3 0.50% -
CaO 3.50% 0.08
TiO2 0.10% -
SiO2 53.50% 1.12
LOI 12.00%n/a
Oxide Weight 109.96
Formula Weight 124.95


Formerly Pioneer Talc. Subsequently it was manufactured and marketed by Natural Minerals (using the same C-98 name).

AMTAL C-98 was a white-firing talc used as a flux, filler and thermal expansion modifier for traditional, refractory and technical ceramic applications (wall and floor tile, tableware, sanitaryware, electrical Insulators, porcelain, hobbyware ). It is also used in technical ceramics where it functions as the major silicate material replacing clays and feldspars in lower grade alumina products such as steatite ceramics and low-expansion cordierite materials.

AMTAL C-98 was also an economical source of MgO is glazes.

The powder was grey (as opposed to white of many other talcs) because the material contained some amorphous carbon.

Related Information

American Talc C-98 bag

Texas talc (left) and Montana talc (right)

Texas talc contains some amorphous carbon. The carbon is not stand-alone, but as CO2 in the dolomitic part of the ore. It produces ~7% LOI between 750-850C. Even though the powder color is so much darker in the raw form, it fires whiter! But there is more going on here. On paper, both contain about 0.5% Fe2O3. But the iron species in the two talcs are different. In Texas talcs, the iron is part of the crystal lattice. But, in the Montana material, that 0.5% Fe2O3 is an external iron oxide mineral species, a physical contaminant. While the Montana material fires much darker because of this that iron seems to have little affect on the color of the raw white powder.


Materials Talc
A source of MgO for ceramic glazes, a flux or thermal expansion additive in clay bodies, also used in the manufacture of cordierite.
Materials Pioneer 2661 Talc
Materials Suzorite 325-PE
Materials Natural Talc C-98
Hazards Talc Hazards Overview
Talc is invaluable in the ceramics industry, it is used as a glaze and body ingredient and as a parting a release agent in various processes. Is it safe?
Phlogopite Mica at Wikipedia
Replace Talc with Nepheline Syenite in low temperature white bodies
Typecodes Flux Source
Materials that source Na2O, K2O, Li2O, CaO, MgO and other fluxes but are not feldspars or frits. Remember that materials can be flux sources but also perform many other roles. For example, talc is a flux in high temperature glazes, but a matting agent in low temperatures ones. It can also be a flux, a filler and an expansion increaser in bodies.
By Tony Hansen
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