Talc

Talc is the softest rock in the world. While most people think of talc as a white substance, it can be gray, green, blue, pink and even black.

How talc is formed
Talc deposits are the result of the transformation of existing rocks under the effect of hydrothermal fluids carrying one or several of the components needed to form talc. Movement in the Earth's crust (tectonics) enable hydrothermal fluids to penetrate the rock, creating a micro-permeability that enables reactions in the rock mass. This produces talc.

The size and shape of talc deposits depend on the intensity of the hydrothermal activity. Pressure and deformations, both during and after this transformation, determine the crystallinity of the talc ore within the deposit. Hence, talc deposits can differ according to the parent rock from which they are derived. There are four main categories of talc deposits:

Magnesium carbonate derivative ore bodies
Serpentinite derivative ore bodies
Siliceous or silico-aluminous rock derivative ore bodies
Magnesium sedimentary deposit derivative ore bodies

Talc production
Most talc deposits are mined using the open pit technique. The overburden (surface rock) covering the talc deposits is removed using giant shovels that can shift up to 1,500 tonnes of rock per hour.

Talc is extracted from the seam using shovels. At this stage, the different ore types are sorted as they are extracted from the seam.

The sorting of different talc ores according to talc content and brightness is an important stage in the production of talc. Sorting techniques include hand sorting, using state-of-the-art laser and image analysis technology or using flotation.

Talc ore is then milled to obtain the right particle size, distribution curve and top cut for specific applications. Milling techniques include using compressed air, steam and impact grinding. The median particle size can range from less then one micron to 15 microns, with top cuts from six microns to over 100 microns.

Certain grades of talc are treated, for example amine-coated talc used in fertilisers, silane-coated talcs used in the rubber industry and cationic talc for pitch control in papermaking. Talcs used for cosmetics and pharmaceutical industry are heat-treated to decontaminate them.

Talc powder is usually packaged and delivered in bags, semi-bulk bags or in bulk. There has also been an increased demand for talc in pellet form or in slurry form.

Uses for talc
Talc is used in the manufacture of a wide range of everyday products including animal feed, automobiles, cables, sweets, ceramic tiles, chewing gum, cosmetics, fertilisers, foundry technology, olive oil processing, paint, paper, pharmaceuticals, plaster, plastics, printing inks, putties, refractories, roofing, sanitary-ware, tyres and of course body powder.

Further information about talc production by Rio Tinto's subsidiary, Luzenac, visit the Rio Tinto Minerals website. For more information on our other products, see our corporate fact sheets.