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Ignimbrites are associated with nearly most of the world's volcanoes and are defined as a deposit from pyroclastic density currents. They consist predominantly of pumiceous lapilli and blocks, and glass shards, which shows evidence of having been emplaced as a concentrated hot and dry particulate flow. These rocks are widely used as building stone especially in ancient buildings. Bitlis valley is covered by ignimbritic products, derived from Nemrut stratovolcano, one of the significant volcanic centers in Eastern Anatolia. The Bitlis ignimbrite is separated into lower level (LL), middle level (ML) and upper level (UL) according to color, welding degree and structural features. All three levels were used extensively in many parts of the Bitlis castle as masonry materials. Studies were carried out on mineralogical and geochemical composition and on physical and mechanical properties of the ignimbrites. In addition, a freeze-thaw cycle test was executed. There are no considerable differences in mineralogical composition among the levels of ignimbrite. All levels contain plagioclase, sanidine, pyroxene, and opaque mineral. In addition, anorthoclase and quartz are seen. In general, the LL of ignimbrite shows relic perlitic and eutaxitic texture, whereas eutaxitic and vesicular texture are commonly developed in the ML and UL, respectively. Lower, middle, and upper level ignimbrite samples display similar and limited compositional spread in terms of major oxide elements. They have trachyte composition. Building stones can be classified according to mineralogy, mechanical and physical properties and processing types. Mechanical and physical properties are very important with respect to stone quality/durability. The mechanical and physical properties of the ignimbrites are controlled by the welding degree. It was found that increasing welding degree from UL to LL correlates with increasing density, compressive strength and slake durability index and with decreasing porosity. The Bitlis ignimbrites have turned out as susceptible to freeze-thaw cycles.

In the present study, the properties of calcium carbonate mineralization and urease and carbonic anhydrase activities of Bacillus amyloliquefaciens U17 isolated from calcareous soil of Denizli (Turkey) were analyzed. CaCO 3 was produced in all growth phases. Strain U17 showed 0.615 ± 0.092 µmol/min/mg urease enzyme activity in calcium mineralization medium and 1.315 ± 0.021 µmol/min/mg urease enzyme activity in Luria-Bertani medium supplemented with urea, whereas it showed 36.03 ± 5.48 nmol/min/ mg carbonic anhydrase enzyme activity in CaCO 3 precipitation medium and 28.82 ± 3.31 nmol/min/mg carbonic anhydrase enzyme activity in Luria-Bertani medium supplemented with urea. The urease B protein expression level of strain U17 was detected by western blotting for the first time. The produced CaCO 3 crystals were analyzed by X-ray diffraction, X-ray fluorescence, confocal RAMAN spectrophotometer, scanning electron microscopy, and electron probe microanalyzer for the evaluation of their morphological and elemental properties. Rhombohedral vaterite and layered calcite crystals were clearly detected and verified by mineralogical analyses. All these results showed that strain U17 can be used in many engineering and geological applications due to its CaCO 3 precipitation ability.

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