The results of the bulk mineralogical analyses of the studied samples,
as well as their color, suggested uses and pH, are reported in Table 1,
with their X-ray patterns presented in Fig. 1.
The samples are divided into five groups based on type and association
of clay minerals, as described in more detail later. In terms of bulk
composition, all of the samples are characterized by the presence of a
significant non-clay fraction (from ~11 to ~64%) that is represented
by calcite, dolomite, quartz, feldspars and gypsum.