Analyses were carried out on 15 clay samples purchased from local
stores (Table 1). Most of the clays were contained in 0.5 kg sacks.
About 0.5 kg of each sample was weighed and dried in an oven at 30
°C for 24 h. The dried samples were then weighed and homogenized.
The mineralogical analyses were carried out using a Philips X'Change
PW 1830 diffractometer (Cu Ka radiation). Randomly-oriented powders
were prepared by gently hand crushing the bulk samples. The powders
were then side loaded into an aluminum holder to examine the
unoriented powder (bulk composition), and were subsequently analyzed
at a 0.02° step with a counting time of 1 s/step from 2° to 60°