Talc is a magnesium silicate mineral with the simplified molecular formula Mg3Si4O10(OH)2. The talc products used by the coatings industry contain the mineral talc, but also accessory minerals in varying amounts. These include chlorite, serpentine, quartz, tremolite, anthophyllite and carbonates such as magnesite, dolomite, and calcite.
Talc products are described as platy talc, containing predominately (>90%) the mineral talc; or tremolitic talc, most often a natural blend of talc, tremolite, serpentine and anthophyllite. Platy talcs can be further classified as microcrystalline or macrocrystalline. Microcrystalline varieties are naturally small in plate size and comprise compact, dense ores. Macrocrystalline varieties contain relatively large, higher aspect ratio plates.
The so-called western platy talcs, from Montana and Texas, are microcrystalline, with chlorite as a characteristic accessory mineral. Eastern platy talcs, from Vermont and Canada, are macrocrystalline, with carbonates as characteristic accessory minerals, as is the Chinese talc that is readily available in North America.