Talc is a layered, hydrous magnesium silicate mineral. Talc has a soft, soapy feel and a smooth texture. Talc is also known for its insulation, heat resistance, chemical stability, oil absorption and strong covering quality. Talc. Mg_3Si_4O_(10)(OH)_2, has a theoretical chemical composition of MgO at 31.7 percent, SiO_2 at 63.5 percent, and H_2O at 4.8 percent. Talc's chemical composition can vary depending on its geological history/parent rock association. Two key elemental substitutions in the talc crystal structure are iron for magnesium and fluorine for hydroxyl. Pyrophyllite is also a layered, hydrous aluminum silicate mineral. Pyrophyllite has similar physical properties as talc. Pyrophyllite, Al_2Si_4O_(10)(OH)_2, has a theoretical chemical composition of Al_2O_33 at 28.3 percent, SiO_2 at 66.7 percent, and H_2O at 5 percent. Pyrophyllite has minimal elemental substitution compared to talc.
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