Talc (mineral)

Where Found

Talc is a metamorphicrock that occurs in foliated masses as well as in a massive form called soapstone. Major producers include China, South Korea, India, the United States (with Montana, Texas, Vermont, New York, and California the leading states), Finland, Brazil, and Japan.

Primary Uses

Talc is a widely used raw material. The primary uses for talc are in ceramics, paper, paint, roofing, plastics, rubber, refractory applications, cosmetics, house-insulating materials, insecticides, and lubricants. A similar mineral, pyrophyllite, is used in refratories, paint, and ceramics.

Technical Definition

Talc is a common, very soft, hydrous magnesium silicate mineral. The mineral is typically pale green, white, or grayish, with a greasy feel and pearly luster. The presence of iron turns it reddish or brown. Its specific gravity is 2.82. The related mineral pyrophyllite is a hydrous aluminum silicate and occurs in compact masses or foliated form.

Description, Distribution, and Forms

Talc is a metamorphic rock that belongs to the layered silicate group of minerals in which continuous sheets of silicon dioxide molecules are linked together by magnesium atoms to form well-defined electrically neutral layers. The layers are held together by relatively weak forces, so the mineral is extremely soft mechanically. In fact, talc is the standard for softness at the bottom of the Mohs hardness scale; its hardness is one on a scale from one to ten, and it is easily scratched by a fingernail. The foliated appearance of talc is a direct consequence of the basic layered structure of the mineral.

The impure form of talc is known as steatite, or soapstone, the common name coming from the greasy or soapy feeling imparted when it is rubbed between the fingers. Soapstones are composed of talc, serpentine, and carbonates, representing original peridotites that were altered at low temperatures by hydrothermal solutions. When water and silica or carbon dioxide are added to extensively altered olivine- or pyroxene-rich igneous rocks, and when water and silica are added to altered carbonate rocks, talc forms. Talc is also found in crystalline schists. The mineral is found mostly in mountainous regions, with China, South Korea, and Japan as the chief sources. Historically, the Pyrenees Mountains of France were a major source of talc and contributed to the beginning of the cosmetic’s industry in that country.

History

Talc has been used since ancient times for carved and engraved ornaments and utensils. American Indians used steatite for making bowls, pots, and stoves, and Eskimos used it for sculptures. Talc has become an important ingredient in many commercial products.

Obtaining Talc

Generally, talc is obtained through open-pit mining techniques. In his book Functional Fillers for Plastics (2005), Marino Xanthos outlines the seven-to-eight-step process for obtaining talc through open-pit mining. First, the overburden is removed, thus exposing the talc. The talc is then shoveled out of the mine in order to be crushed. Then it is categorized by brightness and content. The talc is ground to break it down further. For most talc this is the final procedure. However, high-grade talcs, such as those used in the pharmaceutical industry, require treatment with various chemical compounds.

Uses of Talc

In the ceramics industry, talc is used in tableware, electrical porcelain, and glazed wall tiles. In paints, talc is used as a extender and as a pigment. It is used as a filler in paper, rubber, insecticides, lubricants, and leather salves. In cosmetics, it is used in toilet powders, soaps, and creams, with its extreme softness leading to its use as talcum powder and face powder. (With revelations that talc in cosmetics might be linked to lung, ovarian, and skin cancers, many consumers began to avoid talc-containing products.) Massive slabs of talc are used for acid-proof laboratory tables, sinks, sanitary appliances, acid tanks, electrical switchboards, mantels, and hearthstones. Because it is a poor conductor of electricity and heat, it is used as insulation and as a roofing material.