| Silica has various polymorphic forms such as quartz,
cristobalite, tridymite, hydrated or opaline silica etc. Oneof
the most fundamental aspects in the characterisation of
any raw material is the identification of the crystalline
minerals present in the same. When X-ray diffraction is
used for the identification of silica minerals, it is difficult
to distinguish between a-cristobalite and certain type of
opaline silica. Two siliceous earth samples, one from
Rajasthan and the other from Tamil Nadu have been
characterised by studying their chemical properties, XRD
and IR spectral analyses, behaviour towards thermal treatment
and chemical reactivity. Both samples were found to
be opaline silica and not a-cistobalite. |
