This author avoids using the mediation of the equivalent sphere. Usually, crystals have three main dimensions A, B and C, so that:
The intermediate dimension B is the only dimension that can be correlated with granulometric analysis by sifting. Consequently, we define the coefficients directly:
Q and E are the volume and the surface of a crystal taken at random. All of the crystals are supposed to be geometrically similar, which ensures the independence of a and P relative to the crystal size.
If the form of the crystals changes through growth, then the growing rate will be:
Note that if R is the rate of orthogonal growth for a face perpendicular to dimension B, the crystal growth rate is:
The importance of form: porosity
The porosity ? of a crystal bed is a direct function of the form. Non-pressed loose fibers 0.9 < ? < 0.99
Loose plates 0.80 < s < 0.9
Irregular but equidimensional particles 0.4< ? < 0.7
Spheres г # 0.4
Tight parallel fibers г # 0.2
A minimum volume is required for explosives. It is advantageous that these particles be spherical.
Silver halide used for photography takes the form of plates due to the very high non-sphericity coefficient for this configuration. These halides offer a maximum surface volume and, for a given quantity of silver, optimal light sensitivity.