The Use of Methylene Blue Adsorption Test to Assess the Clay Content of the Cappadocian Tuff

Fairy chimneys formed within the Cappadocian tuft are important landforms. Some of them were dwelled in the past and contain valuable wall paintings. However, the tuff is chemically and physically deteriorated due to atmospheric effects. the chemical weathering of the volcanic glass of the tuft produces smectite-type clay mineral. Assessment of the clay content of the weathered zones developed within the tuft is essential to understand their engineering behaviour, and thus to take necessary precautions for the purpose of conservation. In this study, the clay content of the tuft is assessed by the "methylene blue adsorption test" using spot method. The method is based on the replacement of the natural cations of clays by methylene blue dye. The amount of the dye adsorbed by the clays is used to calculate first the cation exchange capacity of the tuft and then its clay content. Based on the test results, the clay content of the tuft ranges between 2% and 14%. It is higher adjecent to joints and lower where lichen cover exists.