Silica phase transitions in opal-cristobalite rocks as a factor of quality of siliceous raw material

Relevance of the discussed issue. In diatomite and clayey diatomite during diagenetic transformations, there is a disturbance or partial loss of biomorphic structure, which determines the unique properties of diatomites as raw materials for production of filtering and sorption-active materials. Structure transformation is accompanied as well by the change in material composition due to the polymorphic transitions of silica - opal-A in opal-CT, and at deeper transformations - further into cristobalite, tridymite. The changes in structure and mineral composition inevitably lead to the changes in industrially significant properties of opal-cristobalite rocks: density, porosity, specific surface, mechanical strength, etc. To date, the Russian scientific literature has little information on the fact that technological properties and quality of siliceous raw materials are controlled by the degree of diagenetic transformation, this relationship is not shown as well on the example of specific mineral resource base facilities. The main aim is to analyze the effect of the degree of diagenetic transformations and phase transitions of opal-A in opal-CT in opal-cristobalite rocks on industrially significant properties: porosity, density, specific surface. The methods used in the research: field studies, X-ray fluorescence analysis, scanning electron microscopy, determination of porosity, density, specific surface area (BET method). The results. For the first time, the relationship between the physical properties, chemical composition and phase transitions of silica in rocks is shown for the objects of mineral-raw-material base of opal-cristobalite rocks of the Transuralian region and North Western Siberia. According to the results of the studies carried out, it can be stated that when comparing rocks in different stages of diagenesis, significant differences in the content of silica and sesquioxides are determined. At diagenetic transformations one can observe the growth of silica content and at the same time increase in density, reduction in porosity and change in the specific surface. According to the scanning electron microscopy data, the studied opal-cristobalite rocks were classified into four groups.