How is talc formed?
Talc is an alteration mineral. It is formed by geological modification of some host rock. Most talc is formed from the alteration of dolomite (CaMg(CO3)2 or magnesite (MgO) in the presence of excess dissolved silica (SiO2). Altering serpentine or quartzite can also form talc. The different alteration routes form talcs that have significant differences in chemistry, color, morphology and impurities. Minerals commonly associated with talc are, tremolite [(CaMg3(SiO3)4)], serpentine [(3MgO2SiO22H2O)], anthophyllite [Mg7(OH)2(Si4O11)2)], magnesite, mica and chlorite. The latter is a talc-like mineral in which varying proportions of aluminum are substituted for magnesium in the brucite layer. Other impurities such as dolomite, the calcite form of calcium carbonate (CaCO3), iron oxide, carbon, quartz, and manganese oxide may also be present. Because of the alteration method of formation and the multiple routes of talc formation into talc deposits – even if they are close in distance – can be
