X-ray
diffraction pattern of the SCBA burnt in a laboratory at 600 C
revealed the presence of characteristic quartz peaks, while the
samples burnt at 800 C also showed cristobalite peaks [9].
The formation of cristobalite in these cases is attributed to the transformation
of amorphous SiO2 into crystalline SiO2, since quartz is
not transformed into cristobalite under these conditions. Therefore,
these tests [9] proved the presence of amorphous SiO2 in the SCBA
burned at low temperatures.