Talc is a hydrated magnesium silicate mineral, originating from metamorphic rocks (pyroxenites), ultramafic rocks (peridotites), and from dolomitic marbles, where it is formed by hydrothermal replacement of magnesium-rich materials.
Properties and characteristics of talc
- Mineral name: Talc
- Class: Silicate
- Subclass: Phyllosilicate
- Group: Clay minerals
- Subgroup: Clays
- Geological environment: It is located in metamorphic rocks of the convergent plate limits, the talcum powder It is formed when hot waters carrying dissolved magnesium and silica react with dolomitic marbles or when heat and chemically active fluids alter rocks such as dunite and serpentinite.
- Associated minerals: Gypsum, Quartz, Dolomite, Serpentine
- Chemical formula: (If4EITHER10) mg3(oh)two
- Color: Green, White, Grey, Brown, Colorless
- Luster: Vitreous, pearly
- Stripe: White to pale green
- Cleavage: Basal perfect
- Fracture: Uneven
- Tenacity: Sectile
- Hardness: 1-1.5
- Refractive index: nα: 1,539 – 1,550, nβ: 1,589 – 1,594, nγ: 1,589 – 1,600
- Fluorescence: Non-existent
- Specific gravity: 2.7 to 7.8
- Crystal system: Monoclinic
- Uses: Used as non-stick coating in plastics, additive, ceramics, rubber, lubricant in cosmetic products, paper, paint.
Origin, formation and geological environment
The talcum powder It is formed by alteration of magnesium-rich silicates such as olivine, pyroxene and amphiboles, all of which come from metamorphic rocks such as pyroxenites and peridotites, they are also formed in metamorphic rocks or by hydrothermal processes.
In the alteration of rocks rich in magnesium (peridotites and serpentines), due to the metamorphism present with solutions rich in carbonate and alteration of precursor feldspars, feldspathoids, silica-biogenic, or in poorly crystallized clay minerals.
The origins of the large number of deposits of talcum powder globally are clearly defined by the host rock and accessory minerals found with the talcum powder.
When large amounts of iron (Fe) replace magnesium (Mg), the mineral is known as minesotaite, however, when large amounts of aluminum (Al) replace magnesium (Mg), the mineral is known as pyrophyllite.
How to identify talc?
The talcum powder it can be recognized with the naked eye due to its color and texture, since it is white and to the touch it turns out to be something greasy or soapy that could be similar to the soap that seamstresses usually use and in turn can be scratched with a fingernail.
At first glance it can be easily confused with kaolin, due to its colour, texture or hardness, despite the fact that kaolin is harder than talc, they have similar characteristics and even belong to the group of silicates.
Because the contiguous layers of silica are loosely bound only by van der Waals forces, it is possible that talc can be easily cut along this plane, for this reason it has a naturally slippery feel, lamellar structure, and its smoothness.
Talc is one of the softest minerals, with a hardness of just 1 on the Mohs scale; however, when split on the silica surface, the surface created is antagonistic to water; while when fractured between the silica-brucite-silica layers, the surface created is hydrophilic ionic.
It can be distinguished from other minerals because it is insoluble in acids, however, in the case of pyrophyllite, it is necessary to resort to the use of X-rays or by moistening with a solution of cobalt nitrate, since when it is subjected to heat it subsequently dissolves. it turns pale violet, while the pyrophyllite turns blue.
Uses and applications of talc
- Trace amounts of the mineral are used in the ceramics industry due to a change in firing technology.
- In the paint industry as an additive.
- In the cosmetic industry, it is used in the manufacture of lubricants for cosmetic products.
- In the plastics industry it is used more frequently, as the mineral becomes an important ingredient in automotive plastics.
- The best known uses are in talcum powder.
- Its use in rubber production increased slightly.
- Used in tailor’s soap.
- On certain occasions it is carved to make decorative objects.
Exploration and exploitation
Most of the talc is produced from open pit mines where the rock is partially drilled, mined, and crushed in mining operations.
They are produced through meticulous and selective operations of extraction and classification of high quality minerals.
Being cautious during the extraction process is paramount to avoid contaminating the talc with other rock materials; because these other materials may have an adverse effect on the color of the product.
Contamination can introduce hard particles, causing serious problems in applications where talc is used due to its softness or lubricating properties.
Subsequently, the partially crushed rock is taken from the mine to a mill, where the particle size is reduced, and those impurities are sometimes removed by froth flotation or mechanical processes.
The mills generally produce finely ground talc thus meeting essential parameters in particle size, gloss, composition, and other properties.