Today we are discussing talc. What is talc exactly and why should we use it?
Talc, also called “talcum powder” is not just useful for baby’s bottoms. It is also an industrial mineral used in a variety of industries, from paint to ceramics and cosmetics to soaps. The chemical name for talc is magnesium silicate.
The soft rock it comes from is called “soapstone” since it is soft, soapy and slippery to the touch. Soapstone is popular for carvings and statues since it easily carved into shapes.
Talc is generally known as the softest mineral on earth, coming number one on the Mohs hardness scale of minerals, where diamond is number 10.
| Mohs hardness of minerals | |
|---|---|
| Diamond | 10 |
| Silica | 7 |
| Dolomite | 3.5 |
| Kaolin | 2 |
| Talc | 1 |
Talc is also inert, which means it is chemically unreactive. Its high absorptive properties make it very good at absorbing moisture and oil. The combination of being so soft, inert, absorptive and very white, is what makes it the mineral of choice for use on babies, in cosmetics and for personal use. Its absorptive properties also make it a useful anti-caking agent.
| Oil absorption of minerals (ml/100g) | |
|---|---|
| Kaolin | 45 |
| Talc | 42 |
| Dolomite | 20 |
| Calcium carbonate | 18 |
As you’d expect from minerals that come out of the ground, most of them are hydrophilic, or water-loving. However one exception is talc.
| Oil absorption of minerals (ml/100g) | |
|---|---|
| Titanium dioxide | Hydrophilic |
| Calcium carbonate | Hydrophilic |
| Talc | Hydrophobic |
| Kaolin | Hydrophilic |
| Dolomite | Hydrophilic |
So if you are making a waterproofing compound that must repel water, you might choose talc over kaolin, for example. Its hydrophobic nature also makes it a suitable filler for plastics.
A hydrophilic mineral loves water, so it wets well and disperses easily and quickly into water. A hydrophobic mineral like talc tends to sit on the surface of the water and does not want to mix. Luckily it can usually be persuaded with vigorous mixing, to disperse into water.
Talc particles are platelets, which makes it a pretty slippery character. This is why it is used in many industries as a lubricant and for anti-stick properties. For example, it is used to stop sheets of rubber from sticking to each other, and by gymnasts to keep their hands dry.
In the building industry it can be used for reinforcement and as an electric and heat insulator.
Talc is popular as a filler to cheapen various other items, such as bars of toilet soap.
Talc and asbestos
Talc has had some bad press because there are some talc deposits that contain asbestos. However for many years now, all pharmaceutical and cosmetic grades of talc as well as most industrial grades have been certified asbestos-free. For example, our ASCOM T20 talc data sheet says “Asbestos: Nil”
When is talc NOT talc?
We have come across some talc that has been diluted with calcite to make it cheaper. So it is not pure talc, it is a mixture. How can you find out whether you have a pure talc or not? Here are some tips:
- If the price is much cheaper than other talcs, that could be a clue.
- Check the data sheet for the CaO content. Pure talc should have less than 1% CaO. If you see a bigger number like 16%, then your talc most likely contains calcite.
- Pour some vinegar on a small sample. If it fizzes, then you have calcite in your talc!
So be vigilant, it’s not just the talc itself that’s a slippery character!