Talc is the magnesium silicate structural analog to pyrophyllite. Its properties are nearly identical to pyrophyllite, except that Al3+ cations have been replaced by Mg2+ cations . Talc occurs in secondary deposits and is formed by the weathering of magnesium silicate minerals such as olivine and pyroxene . In bulk form, talc is also called soapstone and steatite. A typical composition for talc is given in Table 7 . Historically, talc has been used extensively in electrical insulator applications, in paints, and as talcum powder .