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MODELS OF STATIC GEOLOGIC SYSTEMS 213

Fig. 11.6. Classification of Kirmaku (a, c) and Podkirmaku (b, d) clastic rocks in SE (a, b) and NW (c, d)
parts of Absheron Archipelago, Azerbaijan (after Buryakovsky et al., 2001). 1 – sand, 2 – silty-clayey
sand, 3 – loam, 4 – silt, 5 – unsorted sediments, 6 – clayey-loam, 7 – sandy-silty shale, 8 – shale.

Thus, on the basis of their heterogeneity, the rocks can be classified and rated
quantitatively. A rock with the relative entropy below 0.5 can be considered as a very
homogeneous one, composed of grains of about similar size. The poorly sorted rocks
have a relative entropy higher than 0.5.
In calculating the entropy, only the frequencies (probabilities) of every component
of the system are taken into account; the absolute magnitudes of the components are
not considered. This may be a shortcoming when the properties of a mixture depend
upon the absolute contents of its components (or of their ratios); for example, where
the porosity of a mixture depends not only on the proportions of various fractions in
the rock, but also on the mean diameter of the grains in every fraction. In such a
case, the most heterogeneous rocks, with the lowest porosity, will not fall in the
center of the triangle but will be somewhere between the fractions with the largest
and smallest mean diameters of grains.
The merit of rating the indefiniteness or heterogeneity of a real system by means
of its entropy lies in its quantitative expression by one single number and not by
several numbers (three or even more).
The use of relative entropy has another advantage, because its magnitude has the
upper and lower limits (0pH r p1). The other parameters of heterogeneity of a