talc - Formation, Occurrence, Uses, Safety

A hydrous magnesium silicate mineral (Mg₃Si₄O₁₀(OH)₂), formed in metamorphic rocks as light-grey soft masses; also known as steatite or soapstone. It may be associated with serpentine. There are large deposits in Austria and India. It is used in cosmetics (talcum powder) and in the paper, paint, rubber, and textile industries. It may also be carved for ornaments.

Talc is a mineral composed of hydrated magnesium silicate with the chemical formula H2Mg3(SiO3)4 or Mg3Si4O10(OH)2.

Formation

Talc is a metamorphic mineral resulting from the metamorphism of magnesian minerals such as pyroxene, amphibole, olivine and other similar minerals in the presence of carbon dioxide and water. This is known as talc carbonation and produces a suite of rocks known as talc carbonates.

Talc is primarily formed via carbonation of serpentine, via the following reaction;

Serpentine + Carbon Dioxide → Talc + Magnesite + Water

Talc can also be formed via a reaction between dolomite and silica, which is typical of skarnification of dolomites via silica flooding in contact metamorphic aureoles;

Dolomite + Silica + Water → Talc + Calcite + Carbon Dioxide

Talc can also be formed from magnesian chlorite and quartz in blueschist and eclogite metamorphism via the following reaction:

Chlorite + Quartz → Kyanite + Talc + H2O

In this reaction, the ratio of talc and kyanite is dependant on aluminium content with more aluminous rocks favoring production of kyanite.

Occurrence

Talc is a very common metamorphic mineral in metamorphic belts which contain ultramafic rocks and within whiteschist and blueschist metamorphic terranes.

Talc carbonated ultramafics are typical of many areas of the Archaean cratons, notably the komatiite belts of the Yilgarn Craton in Western Australia.

Notable economic talc occurrences include the Mount Seabrook talc mine, Western Australia, formed upon a polydeformed layered ultramafic intrusion.

Uses

A coarse grayish-green talc has been called soapstone or steatite and has been used for stoves, sinks, electrical switchboards, etc. Talc is used in baby powder, an astringent powder used for preventing rashes on the area covered by a diaper (see diaper rash).

Talc is also used as food additive or in pharmaceutical products.

Talcum powder has also become widely used as a stretching substance for marihuana.

Safety

Several studies have established preliminary links between talc and pulmonary issues, lung cancer, skin cancer and ovarian cancer. However, no conclusive study has yet been made to determine either the toxicity and/or carcinogenic nature of talc and the long history of safe use suggests that these concerns are unfounded.

The U.S. Food and Drug Administration (FDA) considers non-asbestiform talc, that is talc which does not contain potentially carcinogenic asbestiform amphibole fibers, to be Generally Recognized As Safe (GRAS) for use in cosmetics.