Have you ever thought about the shape of different mineral particles, and what impact the particle shape has on a particular mineral’s performance? In many industries where minerals are used as fillers or opacifiers, the shape of the particle is very important, especially in terms of how much opacity one mineral delivers compared to another. The industries where this is particularly significant are the paint and paper industries, but particle shape can also have a bearing in rubber, adhesive and other applications.

Simplistically speaking, commonly-used mineral particles can generally be described as either platy (plate-like), or round. I use the term “round” loosely to describe particles that have similar dimensions of height, width and length, so a cube or a rhombic shape, for example, would both be included in this simplistic definition of round. If you want to remember which one kaolin is, you only need to refer to the Serina Kaolin logo to remind you:

As you see, we have incorporated a stylised kaolin platelet into our logo. Some common minerals and their general particle shape are given in this table:

Platy particles Round particles
KaolinCalcium carbonate
TalcDolomite
PyrophylliteSilica
MicaFeldspar

Platy particles in general give better hiding power (or opacity) than round particles. Imagine the platelets as a number of tiles lying on top of each other. Then it is quite easy to understand that this pile of tiles would block out the light better than a pile of the same number of round balls. Or if you want to block the light to the same extent, you probably need a larger number of round balls to get the same effect as the tiles.

So the general conclusion then, is that if you want to increase your opacity, go for the platy rather than the round mineral shape.

Interestingly, the production of synthetic precipitated calcium carbonate has now advanced to a point where the manufacturers now claim they can “engineer” a calcium carbonate particle with a platy shape (amazing what they can do these days.)

In some industries, however, the mineral shape has no bearing. Take ceramics, for example. Here what is important is the chemical composition of the mineral because everything gets melted together at high temperature. Particle size probably has more relevance than particle shape.

Would you like to see a paint formulation which contains no TiO2?

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