|Hnúšťa -Mútnik, Slovakia (The length of the geologist's hammer at the bottom of the picture is 28 cm.)|
|General and classification|
(and possibly department)
|Silicates and Germanates|
System no. to Strunz
and to Dana
|9th EC.05 ( 8th edition : VIII / H.09)
|Crystal system||triclinic or monoclinic|
|Crystal class ; symbol||Talk-1A: triclinic pinacoidal; 1 Talk-2M: monoclinic prismatic; 2 / m
|Space group||P 1 (No. 2)|
a = 5.291 Å ; b = 9.460 Å; c = 5.290 Å,
α = 98.68 °; β = 119.90 °; γ = 85.27 °
|Formula units||Z = 2|
|Density (g / cm 3 )||2.58 to 2.83|
|Break ; Tenacity||uneven|
|colour||colorless, white, gray, greenish, yellowish|
|transparency||translucent to opaque|
|shine||Pearlescent, greasy luster|
n α = 1.538 to 1.550
n β = 1.589 to 1.594
n γ = 1.589 to 1.600
|Birefringence||δ = 0.051|
|Optical character||biaxial negative|
|Axis angle||2V = 0 to 30 °|
|Pleochroism||no, e.g. Partly colorless – pale green|
|Chemical behavior||insoluble in dilute acids and alkalis,
insoluble in water and organic solvents
The mineral talc (not to be confused with the intestinal fat tallow ), in powdered form also known as talc , is a very common layered silicate with the chemical composition Mg 3 [(OH) 2 | Si 4 O 10 ] and therefore chemically natural occurring magnesium silicate hydrate .
Depending on the modification, talc crystallizes as talc-1A in the triclinic or as talc-2M in the monoclinic crystal system and develops mainly leafy, massive or coarse mineral aggregates , very rarely macroscopically recognizable, tabular or pseudotrigonal-pyramidal crystals of mostly matt white or pale green color . Similarly, talc is in the form of pseudomorphic to quartz or anthophyllite .
Etymology and history
Soapstone and thus also talc have been known since ancient times. The linguists suspect that the name originally comes from the Persian language and was then adopted via the Arabic talq in the entire Indo-European language area. Some Upper German dialects still use the terms “talket” and “talkert” to describe the characteristic soft or unstable .
Already in the outdated 8th edition of the mineral classification according to Strunz , talc belonged to the mineral class of "silicates and germanates" and there to the department of "phyllosilicates", where together with pyrophyllite it forms the "pyrophyllite talc group" with the system -No. VIII / E.04 and the other member Minnesotaite .
In the last revised and updated Lapis mineral directory by Stefan Weiß in 2018 , which, out of consideration for private collectors and institutional collections, is still based on this classic system of Karl Hugo Strunz , the mineral was given the system and mineral number. VIII / H.09-40 . In the “lapis system” this also corresponds to the “phyllosilicates” department, where talc, together with ferripyrophyllite , kegelite , macaulayite , minnesotaite, pyrophyllite and willemseit, forms an independent but unnamed group.
The 9th edition of Strunz's mineral systematics , which has been in effect since 2001 and was updated by the International Mineralogical Association (IMA) until 2009, also classifies talc in the “layered silicates” department. This is, however, further subdivided according to the type of stratification, so that the mineral, according to its structure, can be found in the subsection "Layered silicates (phyllosilicates) with mica sheets, composed of tetrahedral and octahedral networks", where it can only be found together with Minnesotaite and Willemseit "Talk group" with the system no. 9.EC.05 forms.
The systematics of minerals according to Dana , which is mainly used in the English-speaking world , also assigns the talk to the class of "silicates and Germanates" and there in the section of "layered silicate minerals". Here it is together with brinrobertsite , ferripyrophyllite, minnesotaite, pyrophyllite and Willemseit in the "pyrophyllite talk group" with system no. 71.02.01 can be found in the subsection “ Layered Silicates: Layers of six-membered rings with 2: 1 layers ”.
Talc-1A crystallizes triclinically in the space group P 1 (space group no. 2) with the lattice parameters a = 5.291 Å ; b = 9.460 Å; c = 5.290 Å; α = 98.68 °; β = 119.90 ° and γ = 85.27 ° as well as two formula units per unit cell .
Talc-2M crystallizes monoclinically in the space group C 2 / c (No. 15) with the lattice parameters a = 5.287 Å; b = 9.158 Å; c = 18.95 Å and β = 99.30 ° as well as four formula units per unit cell.
Pure talc is colorless or white due to lattice defects or microcrystalline formation in massive aggregates. However, it can also be gray, light to dark green or yellowish in color due to foreign admixtures. Other colors are possible as a mineral mix in the soapstone.
physical and chemical properties
Talc has the lowest possible Mohs hardness of 1 and is therefore a reference mineral on the Mohs hardness scale. Due to its low hardness, it is often prone to stacking faults in the crystal structure.
The mineral is water resistant and feels soapy or greasy, so he is often synonymous as bacon stone called.
In leafy and coarse-scaly aggregate forms, talc shows a very perfect cleavage with a mother-of-pearl- like sheen on the cleavage surfaces. Talc is transparent to translucent in thin leaves. Individual leaflets are mildly flexible. Talc is also very similar to mica in terms of optical and other properties .
Talk is a poor conductor of heat and electricity. In front of the soldering pipe, the mineral flakes up due to the action of heat, glows strongly and becomes fireproof after the crystal water has been driven out . Its Mohs hardness increases to 6. When heated to over 800 ° C, more precisely between 800 and 840 ° C, talc (Mg 3 Si 4 O 10 (OH) 2 ) breaks down into the minerals cristobalite (SiO 2 ) and enstatite (Mg 2 [ Si 2 O 6 ]) as well as water vapor (H 2 O) according to the reaction equation:
Modifications and varieties
Education and Locations
Talc is mostly formed secondarily by converting minerals that are free or low in aluminum oxide such as olivines or enstatite , but also metamorphic rocks such as B. marble , metaultrabasites and dolomite up to about 500 ° C or hydrothermal in corridors . Accompanying minerals include actinolite , anthophyllite , calcite , chlorite , dolomite , pyroxene , serpentine , tremolite and vermiculite .
So far (as of 2011) almost 2300 sites are known worldwide. Worth mentioning are the Brumado sites in the Brazilian state of Bahia , where tabular crystals up to two centimeters in size were found, as well as the Gotthard massif in Switzerland with finds of pseudomorphoses of quartz.
In Germany, the mineral occurs in the Black Forest in Baden-Württemberg, in Franconia , Lower Bavaria and the Upper Palatinate in Bavaria, in the Hessian Odenwald , in the Lower Saxony and Thuringian Harz Mountains , in the Sauerland and Siegerland in North Rhine-Westphalia, at several sites in Rhineland-Palatinate , in the Ore Mountains and in Upper Lusatia in Saxony and in the Thuringian Forest .
Other rich localities (three or more regions) include Australia , Brazil , China , Finland , France , India , Italy , Japan , Canada , Madagascar , Mexico , Namibia , Norway , Austria , Peru , Russia , Zambia , Sweden , Switzerland , Zimbabwe , Slovakia , Spain , South Africa , South Korea , Hungary , the United States and the United Kingdom (Great Britain).
Talc is versatile due to its special properties (soft, water-repellent) and is preferably used in powdered form as a lubricant with a low abrasion effect or added to substances in order to give them water-repellent or sealing properties.
Finely ground talc - then often referred to as talc - is used on the one hand as a filler in the industrial production of paper and cellulose , paints and varnishes , as well as rubber, plastic and ceramic goods. Talc is also used as a separating agent in electrical cables (between various elements of the insulation and sheath), in vehicle tires with hose, on elastomers such as the rubber lip seal of car doors, as a light-colored lubricant for shop guides made of plastic or wood. Talc has the advantage of being light in color and easy to wash out of clothing, while black graphite powder is more used to lubricate metal-to-metal sliding surfaces, which already tend to become darker on their own.
In the plastics industry , talc-based reinforcing or fillers are used, for example, to reinforce polyolefins such as HDPE or PP , in the automotive or construction industries. At the end of the 1960s, talc (TV) and glass fiber reinforced (GFV) products based on PP were offered for the first time. Polypropylene compounds reinforced with talc have been used in a wide range of applications since around 1975. The talc content can be 7-55%.
Talc or ground soapstone is the raw material and main component of the technical ceramic steatite , an insulating material frequently used in electrical engineering , e.g. B. for fuse links and insulators .
Talcum powder is used in many products in powder base in cosmetics, such as in baby powder and other body and face powders such as blushes, bronzers, deodorant powder, rouge or kohl pencils and Lipliners. Parents used to powder their children in the diaper area to dry the skin and prevent reddening of the skin or diaper rash . Due to the modern, highly absorbent disposable diapers that are now widely used, powdering the diaper area of babies is now unnecessary.
In medicine it is used for pleurodesis (deliberate, permanent bonding of lung and pleura ) is used (Talkumpleurodese). It is specially made for medical purposes, is sterile and guaranteed asbestos-free . Another special feature is a defined grain size. This prevents the talc powder from migrating to other tissues.
In addition, talc or talc in the pharmaceutical industry both as a powder base and as a lubricant used in the tablet manufacture. It is used in dentistry as a filler for rigid impression materials such as thermoplastic compositions. Talcum powder is also used as a release agent in the manufacture of diaphragms, condoms and ("powdered") latex gloves, unless other release agents or lubricants are used.
Other uses (selection)
- Talc is used as a dry lubricant and release agent
- in apparatus gymnastics (on the horizontal bar, parallel bars, horse ...) for sweat-tolerant drying of the hands. When climbing is talcum powder, however, does not apply; Magnesium carbonate , known as magnesia or chalk, is used to achieve a high coefficient of friction .
- to prevent latex or rubber products from sticking together, such as bicycle tires and tubes , balloons and braided bungee ropes made of latex threads, in order to prevent " eating " at points of contact
- for lubricating the leg and arm cuffs of drysuits to make them easier to put on
- for smoothing dull dance floors and for treating sticky playing cards
- to prevent squeaky shoes due to the friction between the removable sole and the insole
- as a release agent when casting pewter figures in the mold, so that the figure can later be removed more easily
- as escape protection when keeping ants in the Formicarium
- Due to its low abrasive effect, talc is used as a basis for particularly gentle abrasive agents .
- Talc is also used as an extender for marijuana to make it heavier and look resinous at first glance. Smoking talc-enhanced marijuana, however, is said to be highly hazardous to health. Side effects noted in a single case were headache , nausea / vomiting , cough , respiratory problems , circulatory problems and tremors .
- Carrier for pesticides (insect powder)
- Carrier for paint at Holi festivals
- Tailor's chalk , as 3 or 4-cornered, rounded discs with up to 60 mm side length and a flat edge or typically 4 mm thick leads in lead holders, colored white or different colors
- Chalk on rough, oxidized metal
- Part of colored pencils
Precautions and Risks
Inhalation of the powder
Inhaling fine talc powder can lead to inflammation in the peripheral airways, which can lead to so-called foreign body granulomas (see also: pneumoconiosis ). The Federal Institute for Risk Assessment also recommends a ban on the use of baby powder, because the fine powder can cause serious lung damage in young children if it is accidentally inhaled in large quantities. Records since the early 1980s have shown that several thousand young children die or become seriously ill each year after accidentally inhaling powder dust. The use of products containing talc should therefore be avoided as completely as possible.
Granuloma formation on the skin
Granuloma formation also occurs on the skin if too coarse-grained powder (particle size> 100 µm) is used. This is particularly problematic with open wounds.
For decades, numerous studies and counter studies have dealt with a possible cancer risk . Health problems are to be expected with fibrous talc, which has a similar effect to asbestos . Talc containing fibers must therefore not be used for pharmaceutical purposes. It has also been shown that talc particles can cause tumors in the ovaries and lungs. However, it is unclear to what extent cosmetic products are carefully checked.
In 2006, the International Agency for Research on Cancer classified talcum powder as a possible carcinogen when used in female intimate areas.
One study showed that women who use talcum powder in the genital area frequently (between once a week and daily) have a 40% higher risk of developing ovarian cancer. The use of products containing talc should therefore be avoided as completely as possible.
In contrast, the Jena expert and head of the Department of Pneumology and Allergology / Immunology at the Jena University Hospital, Professor Claus Kroegel, sees no connection between talc and cancer. He considers the assessment that talc is highly carcinogenic and dangerous like asbestos to be the result of a widespread error. According to recent studies, talc in its original form was contaminated with asbestos . Accordingly, its use resulted in an increased risk of cancer due to the asbestos content. However, the talc used nowadays is asbestos-free in its purified form and therefore not carcinogenic.
The US cosmetics company Johnson & Johnson was sentenced by a US court in February 2016 to 72 million dollars (around 65 million euros) in damages for a lack of warnings on its talc-containing products . The relatives of a woman who died of ovarian cancer in October 2015 and who had used the company's powder for decades had sued. Baby powder made from talc has been in the Johnson & Johnson range since 1893; the “Shower to Shower” powder was sold in 2012 to the Canadian company Valeant Pharmaceuticals International. Johnson & Johnson now also offers baby powder made from cornstarch ; However, in contrast to talc, moist corn starch can provide a breeding ground for yeasts.
In 2017, Johnson & Johnson had to pay a cancer patient in California around 350 million euros. A court in Los Angeles imposed the record fine on the global corporation.
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