Publishing Date: 2007

E-ISSN: 2147-9364

Volume 22 Issue 1-2


The study area is located in southeast of the town of Sivrihisar (Eskişehir, Central Anatolia). The rocks (Neogene Age) located in the study area is divided into two lithostratigraphic units, namely İlyaspaşa (Lower-Middle Miocene) and Sakarya (Upper Miocene-Pliocene) formations. Sakarya formation is the subdivided into four members namely Gypsum, Lower Limestone, Clayey Dolomite and Upper Limestone. Gypsums show different crystal habit as lenticular, discoidal, rosette and swallow-tail in the field. Gypsum crystals are seen as massive levels, bedded gypsum, fracture filling and scattered within dolomite. Massive and bedded gypsum which interbedded with dolomite layers consist of only lenticular and discoidal gypsum crystals. These are white colored and finely crystalline (clay to sand sized). Also other gypsum crystals show different colors as bluish-grayish colored and light brown. Based on X-ray powder diffraction data, the mineralogical associations of all sections comprise mainly dolomite, gypsum, calcite, locally sepiolite, and in a few cases, palygorskite, smectite, illite and kaolinite. Coarse crystalline gypsum occurrences (discoidal, swallow-tail, rosette) contain a higher percentage of clay minerals than the smaller gypsum crystals. The study area has been influenced by freshwater, weak alkaline and alkaline conditions. The SO3 2- contents of clay-sand sized gypsum occurrences are found to be lower than in other gypsum occurrences

Key Words: gypsum; dolomite; lacustrine; Sivrihisar; Eskişehir; Turkey.

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