Yenikoy power plant is a coal-fired electric power station with a 2 x 210 MW production capacity located in Mugla, Turkey. The plant burns a low quality, high calcium lignite, which causes significant operational problems due to slag formation in combustion units over time. This study aimed to characterize the ash deposits taken from one of the boilers of this particular power plant. The samples were collected from different elevations of the boiler and subjected to chemical, mineralogical and micro-textural analyses. Apart from Ca, significant concentrations of Fe, Al and Si were detected in ash deposits. Anhydrite was found to be the dominating crystalline phase and various forms of aluminosilicates, iron-oxide crystals and Fe-Ca bearing phases were also identified in the samples. The deposits basically consist of two layers; the inner layer characterized by a reddish-colored surface with high hematite content and the outer layer which was mostly in gray and light brown color due to the presence of high amount of calcium particles. (C) 2012 Elsevier B.V. All rights reserved.