What is Talc?

Talc is a clay mineral belonging to the phyllosilicate family. It has the empirical formula of Mg₃Si₄O₁₀(OH)₂ and the chemical name of Magnesium silicate hydroxide.

^{Taken from http://mineral.galleries.com}

Talc is composed of layers of silicate - (SiO₄)^-4 and brucite - Mg₂(OH)₂.

It has a uniform composition with little or no atomic substitution. Derived from ultrabasic igneous rocks or found in some soil fractions, it is classified as a low to medium metamorphic rock.

Talc decomposes at 750 degrees centigrade and 1kbar pressure in two steps;

7Mg₃Si₄O₁₀(OH)₂3Mg₇Si₈O₂₂(OH)₂ + 4SiO₂ +4H₂O (1)

Talc anthophyllite(an amphibole) + quartz + vapour

Mg₇Si₈O₂₂(OH)₂7MgSiO₃ + SiO₂ +H₂O (2)

Anthophyllite enstatite + quartz + vapour

Enstatite is more stable above 750 degrees but under equilibrium conditions (eg at 750 degrees) it takes an average of 6 months to become 50% complete.