Talc is a hydrous magnesium 2:1 phyllosilicate mineral with a chemical composition of Mg
3Si
4O
10(OH)
2, which corresponds to a theoretical content of 63.5% de SiO
2; 31.7% of MgO and 4.8% of H
2O. Although the composition of talc usually stays close to this formula, some substitutions occur. Small amounts (<2%) of Ca, Fe, Al or Mn can substitute for Mg; and small amounts of Al (2–4% of Al
2O
3) or Ti can substitute for Si [
1]. Talc may also contain small quantities of other minerals such as magnesium-aluminum-ferrous silicates (chlorites and fibrous amphiboles), and carbonates (calcite, magnesite, and dolomite). Regarding its structure, talc is monoclinic (C 2/c) or triclinic (C −1) and presents a perfect basal exfoliation. When pure, it has a hardness of 1 to 1.5 on the Mohs scale, a specific weight of 2.75 g/cm
3 and a characteristic greasy feel.
Talc can be green, white, gray, brown, or colorless. Its color is clearly related with its purity and defines its commercial grade. Green talc is usually due to the presence of chlorite minerals and dark talc is formed in the presence of organic matter.
Finely ground talc is used as the powder base of many cosmetic products, since it has many interesting properties such as light color, softness, ductility, good luster, lamellar structure with high specific surface area and wide particle size distribution, hydrophobicity (along Si surface), hydrophilicity (fractured along silica-brucite-silica layers), organophilicity, chemical inertness, high lubricant powder, absorption of specific types of oil and fats, heat resistance and high melting point [
2,
3,
4,
5,
6,
7,
8,
9,
10]. The presence of asbestiform minerals and/or heavy metals reduces their commercial value and their possible applications on cosmetic or pharmaceutical forms [
11,
12,
13].
Geology and Genesis of Talc Ore Deposits
Geologically, talc is always associated with metamorphic, hydrothermal, or metasomatic processes that have acted on magnesium-rich rocks like dolomites and mafic or ultramafic rocks. The mineralogical and geochemical nature of talc is clearly defined by the host rocks. For this mineral to be formed it is required: (a) to have magnesium rich host rocks; (b) hydrothermal solutions rich in SiO
2 and (c) presence of structures that favor the circulation of fluids [
14]. In the deposits associated with mafic or ultramafic rocks the metasomatism is important, and we will find the talc to be associated with important amounts of carbonate. One characteristic reaction of the process is 2(Mg
3Si
2O
5(OH)) + 3CO
2 → Mg
3Si
4O
10(OH)
2 + 3MgCO
3 + 3H
2O. These talcs will be generally rich in iron, nickel and chromium.
For the case of talc formation in dolomites, hydrothermalism must be associated with silica-rich fluids. For example: 3(CaMg(CO
3)
2) + 4SiO
2 + H
2O → Mg
3Si
4O
10(OH)
2 + 3CaCO
3 + 3CO
2 [
14].
In Southern Mexico, between the faults of Papalutla and Oaxaca, there are two important metamorphic complexes with small deposits of talc (
Figure 1) and magnesite located inside serpentine bodies: (a) Tehuitzingo-Tecomatlán in Puebla, of Paleozoic age, and (b) Cuicatlán-Concepción-Pápalo in Oaxaca, of Cretaceous age [
15].
In the Tehuitzingo area, the talc ore deposit is associated with a sequence of basic to ultrabasic serpentinized rocks (~7 km long, ~0.5 km thick) and probably related to a protolith of harzburgite composition [
17]. The serpentinite body consists of chlorite schists, talc and magnesite schists, massive serpentinites (lizardite and antigorite mainly with chromite and magnetite), and ultrabasic dykes [
15,
17]. In this sequence of rocks, a minimum of two serpentinization events were identified, the first associated with compressive tectonics and the second (to which talc formation is associated) with a hydrothermal process [
15,
17].
This basic-ultrabasic body is embedded in a metasedimentary greenschist facies sequence, and the talc outcrops, despite having an irregular distribution, are mainly concentrated in the contact area between the basic-ultrabasic body and the metasedimentary sequences.
Regarding its origin, Ortega-Gutiérrez [
18] considered that this serpentinite unit derived from magmatic rocks and should be associated with an allochthonous and dismembered ophiolitic sequence that has more recently been classified as a suprasubduction ophiolite [
19].
The Cuicatlán-Concepción Pápalo complex is located in the Cuicateco terrane, which includes oceanic crust and metatuffs, black shales and metacarbonates in greenschist facies of Upper Jurassic-Lower Cretaceous age [
20].
In the Concepción Pápalo zone, strongly sheared intrusions of diorites and monzonites define a mylonitic belt associated with serpentinites, with N-NE orientation, a maximum thickness of about 300 m and concordant foliation with the enclosing rocks [
16,
17,
20]. Talc is found associated with the serpentinite bodies, which have been interpreted as the altered ultramafic rocks from the root of a volcanic arc [
20].
Mexico produces less than 0.5% of all talc in the world, and currently most of the companies that sell talcum in this country buy it from other countries such as USA, China or Australia which are some of the leading producers in the world. In 2017 and 2018, according to the mining yearbook of the Mexican Geological Service [
21], the only states producing talc were Guerrero (89%), Baja California (4.6%), Zacatecas (3.8%) and Guanajuato (2.5%). The production of talc in the country has decreased from 11,392 tons in 2016 to 1280 tons in 2017 and then incremented again to 5917 tons in 2018. There has also been an increase in the importation of talc, so that different companies now buy talc from other countries (mainly USA) and pack it in Mexico selling it as talcum produced in Mexico.
All this leads us to wonder whether talc from some states can be used or not as a raw material for cosmetic products and at the same time review the quality of the different types of talc marketed in the country. Currently, there is no specific standard in Mexico on the quality of a cosmetic talc or a specific protocol to determine whether a talc can be used or not in the manufacture of cosmetic products based on its physicochemical and mineralogical properties. Official Standards (NOM-118-SSA-1994; NOM-199-SSA-2000; NOM-047-SSA-2011) for talc of cosmetic uses indicate that the only requirement is not to contain carcinogenic particles such as asbestos or heavy metals.
The main goal of this work is to characterize the mineralogical and geochemical nature of the talc of two Mexican deposits and compare their quality with respect to talc of different prices (4 of high price and 5 of low-medium price) marketed in this country. It is also intended to review the need to establish new specific regulations to legislate the quality requirements for the cosmetic talc in Mexico.