TheMohs scale of mineral hardness, based onscratchhardness comparison, defines value 1 as the hardness of talc, the softest mineral. When scraped on astreak plate, talc produces a white streak, though this indicator is of little importance, because most silicate minerals produce a white streak. Talc is translucent to opaque, with colors ranging from whitish grey to green with a vitreous and pearlyluster. Talc is not soluble in water, and is slightly soluble in dilutemineral acids.[7]
Talc dominantly forms from the metamorphism of magnesian minerals such asserpentine,pyroxene,amphibole, andolivine, in the presence of carbon dioxide and water. This is known as "talc carbonation" or "steatization" and produces a suite of rocks known astalc carbonates.
Talc is primarily formed by hydration and carbonation by this reaction:
Talc can also be formed via a reaction between dolomite and silica, which is typical ofskarnification of dolomites by silica-flooding in contact metamorphic aureoles:
Talc is also found as a diagenetic mineral in sedimentary rocks where it can form from the transformation of metastable hydrated magnesium-clay precursors such askerolite,sepiolite, orstevensite that can precipitate from marine and lake water in certain conditions.[9]
In this reaction, the ratio of talc and kyanite depends onaluminium content, with more aluminous rocks favoring production of kyanite. This is typically associated with high-pressure, low-temperature minerals such asphengite,garnet, andglaucophane within the lowerblueschist facies. Such rocks are typically white, friable, and fibrous, and are known aswhiteschist.
Talc is a trioctahedral layered mineral; its structure is similar topyrophyllite, but with magnesium in the octahedral sites of the composite layers.[2] The crystal structure of talc is described asTOT, meaning that it is composed of parallelTOT layers weakly bonded to each other by weakvan der Waals forces. TheTOT layers in turn consist of two tetrahedral sheets (T) strongly bonded to the two faces of a single trioctahedral sheet (O). It is the weak bonding betweenTOT layers that gives talc its perfect basal cleavage and softness.[10]
The tetrahedral sheets consist of silica tetrahedra, which are silicon ions surrounded by four oxygen ions. The tetrahedra each share three of their four oxygen ions with neighboring tetrahedra to produce a hexagonal sheet. The remaining oxygen ion (theapical oxygen ion) is available to bond with the trioctahedral sheet.[11]
The trioctahedral sheet has the structure of a sheet of the mineralbrucite. Apical oxygens take the place of some of the hydroxyl ions that would be present in a brucite sheet, bonding the tetrahedral sheets tightly to the trioctahedral sheet.[12]
Tetrahedral sheets have a negative charge, since their bulk composition is Si4O104-. The trioctahedral sheet has an equal positive charge, since its bulk composition is Mg3(OH)24+ The combined TOT layer thus is electrically neutral.[13]
Because the hexagons in the T and O sheets are slightly different in size, the sheets are slightly distorted when they bond into a TOT layer. This breaks the hexagonal symmetry and reduces it to monoclinic or triclinic symmetry.[14] However, the original hexahedral symmetry is discernible in the pseudotrigonal character of talc crystals.[3]
View of tetrahedral sheet structure of talc. The apical oxygen ions are tinted pink.
View of trioctahedral sheet of talc. Yellow spheres are hydroxyl; blue are magnesium. Apical oxygen binding sites are white.
Talc crystal viewed along the [100] axis, looking along the layers of the crystal
Talc is a common metamorphic mineral in metamorphic belts that containultramafic rocks, such assoapstone (a high-talc rock), and within whiteschist andblueschist metamorphicterranes. Prime examples of whiteschists include the Franciscan Metamorphic Belt of the western United States, the western EuropeanAlps especially in Italy, certain areas of theMusgrave Block, and some collisionalorogens such as theHimalayas, which stretch alongPakistan,India,Nepal, andBhutan.
China is the key world talc and steatite-producing country with an output of about 2.2M tonnes(2016), which accounts for 30% of total global output. The other major producers are Brazil (12%), India (11%), the U.S. (9%), France (6%), Finland (4%), Italy, Russia, Canada, and Austria (2%, each).[15]
Notable economic talc occurrences include the Mount Seabrook talc mine, Western Australia, formed upon a polydeformed, layered ultramafic intrusion. The France-basedLuzenac Group is the world's largest supplier of mined talc. Its largest talc mine at Trimouns nearLuzenac in southern France produces 400,000 tonnes of talc per year.
Talcum powderThe structure of talc is composed of Si2O5 sheets with magnesium sandwiched between sheets in octahedral sites.
Talc is used in many industries, including paper making,plastic, paint and coatings (e.g. for metal casting molds), rubber, food, electric cable, pharmaceuticals, cosmetics, and ceramics. A coarse grayish-green high-talc rock issoapstone orsteatite, used for stoves, sinks, electrical switchboards, etc. It is often used for surfaces of laboratory table tops and electrical switchboards because of its resistance to heat, electricity, and acids.
In finely ground form, talc finds use as acosmetic (talcum powder), as alubricant, and as a filler in paper manufacture. It is used to coat the insides ofinner tubes and rubber gloves during manufacture to keep the surfaces from sticking. Talcum powder, with heavy refinement, has been used in baby powder, anastringent powder used to preventdiaper rash (nappy rash). TheAmerican Academy of Pediatrics recommends that parents avoid using baby powder because it poses a risk of respiratory problems, including breathing trouble and serious lung damage if inhaled. The small size of the particles makes it difficult to keep them out of the air while applying the powder.Zinc oxide-based ointments are a much safer alternative.[17]
Due to its low shear strength, talc is one of the oldest known solid lubricants. Also, limited use is made of talc as a friction-reducing additive in lubricating oils.[20]
Talc is widely used in the ceramics industry in both bodies and glazes. In low-fire art-ware bodies, it imparts whiteness and increases thermal expansion to resistcrazing. Instonewares, small percentages of talc are used to flux the body and therefore improve strength andvitrification. It is a source ofMgO flux in high-temperature glazes (to control melting temperature). It is also employed as a matting agent in earthenware glazes and can be used to produce magnesia mattes at high temperatures.
ISO standard for quality (ISO 3262)
Type
Talc content min. wt%
Loss on ignition at 1000 °C, wt %
Solubility in HCl, max. wt %
A
95
4 – 6.5
5
B
90
4–9
10
C
70
4–18
30
D
50
4–27
30
Patents are pending on the use of magnesium silicate as a cement substitute. Its production requirements are less energy-intensive than ordinaryPortland cement (at a heating requirement of around 650 °C for talc compared to 1500 °C for limestone to produce Portland cement), while it absorbs far morecarbon dioxide as it hardens. This results in a negativecarbon footprint overall, as the cement substitute removes 0.6 tonnes of CO2 per tonne used. This contrasts with a positive carbon footprint of 0.4 tonnes per tonne of conventional cement.[21]
Talc is used in the production of the materials that are widely used in the building interiors such as base contentpaints in wall coatings. Other areas that use talc to a great extent are organicagriculture, the food industry, cosmetics, and hygiene products such as baby powder anddetergent powder.
Sterile talc powder (NDC 63256-200-05) is a sclerosing agent used in the procedure ofpleurodesis. This can be helpful as acancer treatment to preventpleural effusions (an abnormal collection of fluid in the space between thelungs and thethoracic wall). It is inserted into the space via a chest tube, causing it to close up, so fluid cannot collect there. The product can be sterilized by dry heat,ethylene oxide, orgamma irradiation.[22]
Suspicions have been raised that talc use contributes to certain types of disease, mainly cancers of the ovaries and lungs. According to theIARC, talc containing asbestos is classified as agroup 1 agent (carcinogenic to humans), talc use in theperineum is classified asgroup 2B (possibly carcinogenic to humans), and talc not containing asbestos is classified asgroup 2A (probably carcinogenic to humans).[23] Reviews byCancer Research UK and theAmerican Cancer Society conclude that some studies have found a link, but other studies have not.[24][25]
The studies discusspulmonary issues,[26]lung cancer,[27][28] andovarian cancer.[29] One of these, published in 1993, was a USNational Toxicology Program report, which found that cosmetic grade talc containing noasbestos-like fibres was correlated with tumor formation inrats forced to inhale talc for 6 hours a day, five days a week over at least 113 weeks.[27] A 1971 paper found particles of talc embedded in 75% of the ovarian tumors studied.[30] In 2018,Health Canada issued a warning against inhaling talcum powder or women's using it perineally.[31]
In contrast, however, research published in 1995 and 2000 concluded that, although it was plausible that talc could cause ovarian cancer, no conclusive evidence had been shown.[32][33] Further, a 2008European Journal of Cancer Prevention review of ovarian cancer and talc use studies pointed out that, although many of them examined the duration, frequency, and accumulation of hygienic talc use, few found a positive association among these factors and some found a negative one: “It may be argued that the overall null findings associated with talc-dusted diaphragms and condom use is more convincing evidence for a lack of a carcinogenic effect, especially given the lack of an established correlation between perineal dusting frequency and ovarian tissue talc concentrations and the lack of a consistent dose-response relationship with ovarian cancer risk." Instead, the authors credited powdered talc with "a high degree of safety.”[34]
Similarly, in a 2014 article published in a leading cancer journal, theJournal of the National Cancer Institute, researchers reported the results of a survey of 61,576 postmenopausal women, more than half of whom had used talc powder perineally. The researchers compared the subjects’ reports of their own talc use with their reports of having had ovarian cancer diagnosed by their doctors, and found, regardless of subjects’ age and tubal ligation status, “Ever use of perineal powder ... was not associated with risk of ovarian cancer compared with never use,” nor was any greater individual cancer risk associated with longer use of talc powder. On this basis, the article concluded, “perineal powder use does not appear to influence ovarian cancer risk.”[35] TheCosmetic Ingredient Review Expert Panel concluded in 2015 that talc, in the concentrations currently used in cosmetics, is safe.[36]
One particular issue with commercial use of talc is its frequent co-location in underground deposits withasbestos ore. Asbestos is a general term for different types of fibrous silicate minerals, desirable in construction for their heat resistant properties.[40] There are six varieties of asbestos; the most common variety in manufacturing,white asbestos, is in theserpentine family.[41] Serpentine minerals aresheet silicates; although not in the serpentine family, talc is also a sheet silicate, with two sheets connected by magnesium cations. The frequent co-location of talc deposits with asbestos may result in contamination of mined talc with white asbestos, which poses serious health risks when dispersed into the air and inhaled. Stringent quality control since 1976, including separatingcosmetic- andfood-grade talc from that destined for industrial use, has largely eliminated this issue, but it remains a potential hazard requiring mitigation in the mining and processing of talc.[42] A 2010 USFDA survey failed to find asbestos in a variety of talc-containing products.[43] A 2018Reuters investigation asserted that pharmaceuticals companyJohnson & Johnson knew for decades that there was asbestos in its baby powder,[44] and in 2020 the company stopped selling its baby powder in the US and Canada.[45] There were calls for Johnson & Johnson's largest shareholders to force the company to end global sales of baby powder, and hire an independent firm to conduct a racial justice audit as it had been marketed to African American and overweight women.[46] On August 11, 2022, the company announced it would stop making talc-based powder by 2023 and replace it with cornstarch-based powders. The company said the talc-based powder is safe to use and does not contain asbestos.[47]
In 2006 theInternational Agency for Research on Cancer classified talcum powder as a possible human carcinogen if used in the female genital area. Despite this, no federal agency in the US acted to remove talcum powder from the market or add warnings.[48]
In February 2016, as the result of a lawsuit againstJohnson & Johnson (J&J), aSt. Louis jury awarded $72 million to the family of an Alabama woman who died fromovarian cancer. The family claimed that the use of talcum powder was responsible for her cancer.
In May 2016, a South Dakota woman was awarded $55 million as the result of another lawsuit against J&J.[49] The woman had used Johnson & Johnson'sBaby Powder for more than 35 years before being diagnosed with ovarian cancer in 2011.[50]
In October 2016, a St. Louis jury awarded $70.1 million to a Californian woman with ovarian cancer who had used Johnson's Baby Powder for 45 years.[51]
In August 2017, a Los Angeles jury awarded $417 million to a Californian woman, Eva Echeverria, who developed ovarian cancer as a "proximate result of the unreasonably dangerous and defective nature of talcum powder", her lawsuit against Johnson & Johnson stated.[52] On 20 October 2017,Los Angeles Superior Court judge Maren Nelson dismissed the verdict. The judge stated that Echeverria proved there is "an ongoing debate in the scientific and medical community about whether talc more probably than not causes ovarian cancer and thus (gives) rise to a duty to warn", but not enough to sustain the jury's imposition of liability against Johnson & Johnson stated, and concluded that Echeverria did not adequately establish that talc causes ovarian cancer.[53][54]
In July 2018, a court inSt. Louis awarded a $4.7bn claim ($4.14bn in punitive damages and $550m in compensatory damages) against J&J to 22 claimant women, concluding that the company had suppressed evidence ofasbestos in its products for more than four decades.[55]
At least 1,200 to 2,000 other talcum powder-related lawsuits were pending as of 2016[update].[51][56]
In 2020 J&J stopped sales of its talcum-based baby powder, which it had been selling for 130 years. J&J created a subsidiary responsible for the claims in an effort to resolve the lawsuits in bankruptcy court. In 2023 J&J proposed a nearly $9bn settlement with 50,000 claimants saying the claims were "specious" but it wanted to move on from the issue, but judges blocked the plans, ruling that the subsidiary was not in financial distress and could not use the bankruptcy system to resolve the lawsuits.[57]
In July 2023 J&J sued researchers who linked talc to cancer alleging they usedjunk science to disparage company's products, while defendants say the lawsuits are meant to silence scientists.[58]
^Harlow, Cramer, Bell; et al. (1992). "Perineal exposure to talc and ovarian cancer risk".Obstetrics and Gynecology.80 (1):19–26.PMID1603491.{{cite journal}}: CS1 maint: multiple names: authors list (link)
^Gruber, James (November–December 2019). "Do Cosmetic Consumers Really Know What Ingredients They Are Using? An Inquiry into the Search for the 'Truth'".Skeptical Inquirer.43 (6): 54.
![Talc crystal viewed along the [100] axis, looking along the layers of the crystal](/mt/?noimg=&dark=on&url=http%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3aTalc_structure.jpg)
