Differentiation Index: A New Proxy for Determining Suitability of Volcanic Rocks for Production of Different Fiber Types

Rock fiber is a suitable alternative material to replace traditional glass fibers used in many applications, and so many manufacturers and suppliers around the world are interested in rock fiber. The geochemical properties of rocks to be used in fiber production are of great importance. Some technological evaluation criteria have been proposed previously according to the geochemical properties of the related natural materials. In this study, a single parameter, namely the Differentiation Index (DI), calculated with normative mineral abundances, is proposed against four parameters [total acidity coefficient (K-total), total acidity modulus (M-total), acidity modulus (M-a), viscosity modulus (M-v)] used in previous studies to determine which type of fiber the rocks are suitable for. In addition, we compared the chemical compositions of the selected volcanic rocks from Sivas and Kayseri provinces (Central Anatolia, Turkey) with those of reference rocks from the literature. Sivas samples are dominantly silica-undersaturated, whereas Kayseri samples are silica-oversaturated with frequent silica-saturated samples in both groups. Mineral norms correlate well with modal abundances of nepheline in Sivas samples, indicating the calculated degrees of silica saturation is representative. The DI shows significant correlation with the four parameters and it distinguishes the reference rocks according to the fiber type to be produced. As a result of the evaluation made using the reference rocks employed in this study, we suggest that the 35-50 DI range represents rocks suitable for continuous fiber production, and rocks with DI of < 35 may be ideal for the production of staple fiber. According to the ranges of DI, while most of the Kayseri samples are recommended for continuous fiber production, both types of fibers can be produced from Sivas lavas.