Talc, or talcum, is a clay mineral composed of hydrated magnesium silicate, with the chemical formula Mg3Si4O10(OH)2. Talc in powdered form, often combined with corn starch, is used as baby powder. This mineral is used as a thickening agent and lubricant. It is an ingredient in ceramics, paints, and roofing material. It is a main ingredient in many cosmetics. It occurs as foliated to fibrous masses, and in an exceptionally rare crystal form. It has a perfect basal cleavage and an uneven flat fracture, and it is foliated with a two-dimensional platy form.
Talc
A block of talc
View of trioctahedral sheet of talc. Yellow spheres are hydroxyl; blue are magnesium. Apical oxygen binding sites are white.
Talc crystal viewed along the [100] axis, looking along the layers of the crystal
Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2Si2O5(OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces.
Oxford Clay (Jurassic) exposed near Weymouth, England
Hexagonal sheets of the clay mineral kaolinite (SEM image, 1,340× magnification)
Structure of clay mineral groups