Figure 1 displays the X-ray diffraction patterns of the
pumice raw material and extracted silica calcined at 800°C
for two hours. The figure shows that the untreated pumice
contains crystalline minerals (Figure 1 (a)), such as clinopyroxene
(diopside, augite or basanite types), forsterite and
other minerals in small quantities, such as apatite and
haematite [1, 22–25]. The strong broad hump, between 15