ABOUT TALC
Talc is the softest mineral found on Earth with a score of 1 on the Moh's hardness scale (diamond being a 10). Talc is a vital part of everyday life. The magazines we read, the polymers in our cars and houses, the paints we use and the tiles we walk on are just some of the products that talc enhances.
Talc is a hydrated magnesium sheet silicate with the chemical formula Mg3Si4O10(OH)2. The elementary sheet is composed of a layer of magnesium-oxygen/hydroxyl octahedra, sandwiched between two layers of siliconoxygen tetrahedra. The main or basal surfaces of this elementary sheet do not contain hydroxyl groups or active ions, which explains talc's hydrophobicity and inertness.
Talc is practically insoluble in water and in weak acids and alkalis. It is neither explosive nor flammable. Although it has very little chemical reactivity, talc does have a marked affinity for certain organic chemicals, i.e. it is organophilic. Above 900°C, talc progressively loses its hydroxyl groups and above 1050°C, it re-crystallizes into different forms of enstatite (anhydrous magnesium silicate). Talc's melting point is at 1500
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 or steatization and produces a suite of rocks known as talc carbonates.
Occurrence
Talc is a very common metamorphic mineral in metamorphic belts which contain ultramafic rocks, such as soapstone (a high-talc rock), and within whiteschist and blueschist metamorphic terranes. Prime examples of whiteschists include the Franciscan Metamorphic Belt of the western United States, the western European Alps especially in Italy, certain areas of the Musgrave Block, and some collisional orogens such as the Himalayas.
Talc carbonated ultramafics are typical of many areas of the Archaean cratons, notably the komatiite belts of the Yilgarn Craton in Western Australia. Talc-carbonate ultramafics are also known from the Lachlan Fold Belt, eastern Australia, from Brazil, the Guyana Shield, and from the ophiolite belts of Turkey, Oman and the Middle East.
Notable economic talc occurrences include the Mount Seabrook talc mine, Western Australia, formed upon a polydeformed, layered ultramafic intrusion.
Uses
A coarse grayish-green high-talc rock is soapstone or steatite and has been used for stoves, sinks, electrical switchboards, etc. Talc finds use as a cosmetic (talcum powder), as a lubricant, and as a filler in paper manufacture. Talc is used in baby powder, an astringent powder used for preventing rashes on the area covered by a diaper. Most tailor's chalk is talc, as is the chalk often used for welding or metalworking.
Talc is also used as food additive. In pharmaceutical products, it can be used as a lubricant and glident in the tableting process. In medicine, talc is used as a pleurodesis agent to prevent recurrent pneumothorax. In the European Community the additive number is E553b.
Safety
Several studies have established preliminary links between talc and pulmonary issues, lung cancer, skin cancer and ovarian cancer. This is a major concern considering talc's widespread commercial and household use. 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.
Concerns that cosmetic talc might be carcinogenic are addressed and shown to lack persuasive scientific support. These concerns are based (1). on several, but not all, retrospective epidemiological, statistically barely significant case-control studies of questionable biological import (Their results lack dose-response relationships, are inconsistent and ambiguous, and are therefore inconclusive. Whether inanimate talc particles can translocate from the perineum to the ovaries, a precondition if they were to cause ovarian cancer, remains unresolved.); (2). on one inhalation study in animals whose results, according to a panel of experts, "cannot be considered as relevant predictors of human risk," a position shared by other experts in the field; and (3). on elevated incidence of lung cancer in pottery workers. These workers were occupationally exposed several decades ago to nowadays impermissible concentrations of aerosols comprising a multitude of industrial dusts. To construe a risk for the consumer of pure cosmetic or pharmaceutical-grade talc under consumer conditions, based on these findings, lacks scientific support. Talc is not genotoxic, is not carcinogenic when injected into ovaries of rats, does not cause cancer decades after pleurodesis, and induces apoptosis in vitro in human mesothelioma cells but not in normal mesothelial cells. There is no credible evidence of a cancer risk from inhalation of cosmetic talc by humans. Considering talc a carcinogen lacks convincing scientific documentation.
Sources:
Wikipedia
NCBI- National Center for Biotechnology Information
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