Composition of talc usually stays close to this generalized formula, some substitution occurs. Small amounts of Al or Ti can substitute for Si; small amounts of Fe, Mn and Al can substitute for Mg; and, very small amounts of Ca can substitute for Mg.
When large amounts of Fe substitute for Mg the mineral is known as minnesotaite. When large amounts of Al substitute for Mg the mineral is known as pyrophyllite.
Talc is usually green, white, gray, brown or colorless. It is a translucent mineral with a pearly luster. It is the softest known mineral and is assigned a hardness of 1 on the Mohs Hardness scale.
Talc is a monoclinic mineral with a sheet structure similar to the micas. Talc has perfect cleavage that follows planes between the weakly bonded sheets. These sheets are held together only by van der Waals bonds which allows them to slip past one another easily.
Uses of Talc
- Plastics: It is mainly used as a filler. The platy shape of talc particles can increase the stiffness of products such as polypropylene, vinyl, polyethylene, nylon and polyester. It can also increase the heat resistance of these products and reduce shrinkage.
- Ceramics: such as bathroom fixtures, ceramic tile, pottery and dinnerware.
- Paint: Most paints are suspensions of mineral particles in a liquid. The liquid portion of the paint facilitates application but after the liquid evaporates the mineral particles remain on the wall. Talc is used as an extender and filler in paints. The platy shape of talc particles improves the suspension of solids in the can and helps the liquid paint adhere to a wall without sagging. Powdered talc is a very bright white color. This makes talc an excellent filler in paint because it simultaneously serves to whiten and brighten the paint. Talc's low hardness is valued because it causes less abrasion damage on spray nozzles and other equipment when paint is applied.
- Paper: Most papers are made from a pulp of organic fibers. This pulp is made from wood, rags and other organic materials. Finely-ground mineral matter is added to the pulp to serve as a filler. When the pulp is rolled into thin sheets the mineral matter fills spaces between the pulp fibers, resulting in a paper with a much smoother writing surface. Talc as a mineral fillers can improve the opacity, brightness and whiteness of the paper. Talc also can also improve the paper's ability to absorb ink.