What is Talc? Talc is a hydrous silicate mineral composed of magnesium (Mg), silicon and oxygen (SiO 2, silica), and water. Its chemical formula is Mg 3Si 4O 10(OH) 2. Talc is relatively pure in composition but can contain small amounts of aluminum, iron, manganese, and titanium. Talc can be white, apple green, dark green, or brown, depending ...