Talc is basically a mineral which belongs to the class of silicates. The formation of talc is achieved when the carbonate sediments undergo through contact metamorphosis. It is also formed when the magmatic rocks which are rich in magnesium undergoes the hydrothermal alteration. The rocks which contain talc are metamorphic in nature and therefore talc is produced as secondary mineral.
Talc is also known as steatite and if we talk in chemical terms then it is called hydrated magnesium silicate. It is essential ingredient of soapstone. The crystals develop massive and leaf shaped aggregates along with the fine particles. Talcum is the grounded talc.
Talc is the softest mineral, and the silicate layers of it are placed on the top of some other layers. But they do not bound with each other through chemical bond due to chemical inertness. Rather, they are bounded with the vander Waals forces which are very weak. Because of this only talc gets platy appearance and also the soapy and greasy characteristics.
Talc in its pure form appears white. If some other substances are added in the talc then the color becomes pink or grey accordingly. The other minerals which are there with it include dolomite, calcite, chlorite, quartz and vermiculite.
In natural crystals, iron can replace the magnesium present and aluminum can replace the silicium in the talc. The trait of talc is that it can absorb organic substances. And with the water, the process is entirely reverse in nature. Talc has the properties that make it insoluble, hydrophobic, chemically inert, acid resistant and also non toxic. It does not have taste and aroma.
Talc formation and deposition:
The formation of talc occurs in separate geological environments. The talc deposits are different from each other on the basis of current composition and also on the parent rock composition from which it is derived. The talc deposits can be categorized into four types. Out of them, the two which contribute to the major world’s talc generation are explained as follows-
Talc formed through Dolomite:
When alteration is done on magnesium carbonate rocks like magnesite and dolomite that are of sedimentary nature at high temperature then the talc is produced. For this, the pressure should be less than earth’s surface. The hot fluid which contains the silica transports it which then reacts with the magnesium and results in the formation of talc. The resultant rocks which are altered are rich in magnesites and dolomites. The mineral composition is – 0-75% carbonates /chlorites, 35-100% talc and 0.1-0.5% quartz.
Talc manufactured from Ultramafic Magnesite rocks:
When hydrothermal alteration is done of magmatic rocks that are magnesium rich then talc is formed. As these contain mafic minerals which are rich in magnesium they are known as Ultramafic rocks.
The process of alteration is in two steps: first the hydration of mafic minerals like olivine is done with the help of H2O influx in the serpentine. Then the second step involves the alteration of serpentine to form talc.
The rocks have talc, chlorite, magnesite, sulfides and many different minerals having very low content of quartz in them.
In this process, crude ore is grinded and crushed before the refining is done by flotation so that the content of talc and its whiteness can be increased. This all is done before using it as a mineral for industries.
Talc can be produced by alumino-silicate rocks. Talc remains stable when the pressure is high and temperature is about 700°C in addition with phengite, Mg-chloritoid. The deposits generally are associated with the accumulation of magnesium carbonate. The talc is also formed by directly transforming the magnesium clays.