Author: Tamer KORALAY, Mehmet ÖZKUL, Halil KUMSAR, Sefer Beran ÇELİK, Kadir PEKTAŞ
Publishing Date: 2014
Volume: 2 Issue: 3
Natural stones such as tuff and ignimbrites are used extensively in many parts of the world as building materials because of light weight, strong, soft enough to be easily given form to useful blocks and perfect insulating properties. Turkey widely hosted welded and non-welded ignimbrites that formed during the Upper Miocene and the Pliocene times. They have been commonly used in historical building which had been built in the Anatolian Selçuklu and Ottoman empires times. The Bitlis ignimbrite is named by Özdemir (2003), Karaoğlu et al (2005) and Özdemir et al (2006) as “Nemrut ignimbrite”. In this paper, we approved that the most densely welded ignimbrite crops out typically along Bitlis valley and the vicinity of Bitlis city leding to use this ignimbrite as the Bitlis Ignimbrite. The Bitlis ignimbrite can be divided into three levels these are lower (LL), middle (ML) and upper (UL). The lower level (LL) shows black to blackish brown and glassy well-welded structure. Moderately welded middle level (ML) is reddish pink colour and has high amount of fiammes. The upper level (UL) of the ignimbrite has grey to greyish pink, weakly welded and rock fragments with different composition. The mineralogical composition of Bitlis ignimbrite is composed of sanidine + plagioclase + pyroxene + opaque minerals and less amount of anorthoclase. Each levels of Bitlis ignimbrite have clear differences in terms of macroscopic and microscopic views. Eutaxitic and relict perlitic texture is dominant in LL samples and this level has more compact structure than ML and UL. The amount of flattened pumice fragments and volcanic glass shards in LL and ML are more abundant than UL. Some chemical indices used for the characterization of the degree of weathering in Bitlis ignimbrite are calculated based on chemical analyses results. From LL to UL, there is an increase of Ruxton Ratio, Weathering Index of Parker and Modified Weathering Potential Index values, whereas a decrease can be observed for Vogt’s Residual Index, Chemical Alteration Index, Alumina to Calcium-Sodium Oxide Ratio and Loss on Ignition values. Building stones can be classified according to their mineralogy, mechanical and physical properties and processing types. Mechanical and physical properties are more significant depending on the stones practice aim. Bitlis ignimbrites are of low density 2.31, 1.88 and 1.63 g/cm3 respectively they also have high porosity ranging between 3.97, 19.11 and 30.3 (%) for LL, ML and UL respectively. Strength of Bitlis ignimbrites are very weak to moderate in compression, 41.12, 25.03 and 15.85 MPa for LL, ML and UL respectively. Slake durability index ranges from high to very high, 98.34 for LL, 98.30 for ML and 97.50 for UL.
Key Words: Ignimbrite, East Anatolia, Bitlis Castle, Chemical Weathering Indices, Mechanic-Physical parameters