Such a useful raw material. But what is dolomite actually, and what is it used for?
Picture of dolomite crystal, courtesy of Wikipedia http://en.wikipedia.org/wiki/Dolomite
Dolomite is calcium magnesium carbonate, usually written CaMg(CO3)2. Since your body needs both calcium and magnesium, you’ll often find dolomite as a mineral supplement. Due to its alkalinity, it is also used in antacid tablets.
One dolomite deposit can vary widely from another. Dolomite should be white, but the deposit’s impurities can change its colour to yellowish, brown or even shades of pink! So if you want a very white dolomite for your textured paints, you need to find a good white deposit.
South African dolomites have high levels of iron oxide which give them a yellowish colour. We need to look to our neighbours like Namibia and Kenya for white dolomites. Then, of course, the transport cost becomes a big part of the delivered price. Lead time and reliability of supply become issues to consider.
A white dolomite can be used to substitute calcium carbonate in certain applications. It has the advantage that it is less soluble than calcium carbonate in acid conditions.
Dolomite is usually used as a filler in paints, flooring and similar applications. Coarser grades are used to provide the texture in textured paints. It sometimes competes with silica in this respect.
However, dolomite is not as hard as silica but not as soft as calcite. It has a hardness of 3.5 – 4 on the Mohs scale:
| Mohs hardness of minerals | |
|---|---|
| Diamond | 10 |
| Silica | 7 |
| Dolomite | 3.5 |
| Calcium carbonate | 2 |
| Kaolin | 2 |
| Talc | 1 |
Dolomite has a different role in ceramics. The magnesium carbonate in the dolomite is an important fluxing agent at higher temperatures. At lower temperatures, dolomite can act as a matting agent.
The iron and titanium impurities in the dolomite need to be low for ceramic applications to avoid off-white firing problems.
Dolomite has lots of other useful applications. It can be used as a concrete aggregate, in plate glass and in horticulture as a source of magnesium.
So keep us in mind for your dolomite needs. We offer South African and Kenyan grades as well as super-white, super-fine dolomite from Greece.
Gotta run, I’m off to take my dolomite tablet!