Fig. 10(a) and (b) shows the microstructure of the samples’ surface sintered at 900 °C containing 30% and 40% rock dust respectively. At 900 °C, the sample tiles have not yet experienced full solid state sintering process since clay particles are existent in Fig. 10 (a, b). However, with increasing amount of rock dust, lowering of clay particles has been observed from figure 10-a to 10-b. In both micrographs a dense mass with some pore space are evident.