The main alkaline fluxes are sodium feldspar, potash feldspar while alkaline earth auxiliary fluxes are calcite, magnesitc, dolomite, sepiolite, palygorskite and talc. The objective of the first part of study is to discover firing behavior of magnesite-rich clay within the Ca-rich ceramic bodies. The physical properties, including water adsorption (WA), firing shrinkage (FS) and firing-bending strength (BS) were determined. Replacing the opening materials (grog, sand and marble) with magnesite rich clay (Eskisehir clay) at the ratios of 3, 6, 9, 11, 12, 15 % has effect on firing shrinkage water absorption and bending strength. Eskiehir clay increases bending strength and firing shrinkage. The body containing 15 mass % Eskisehir clay had WA: 15.51, FS: 3.80 and BS: 272.39kgf/cm(2) after firing at 1150degreesC. As the peak temperature is raised within the range of 980degreesC-1250degreesC, the crystalline constituents were identified as quartz, anorthite, gehlenite, diopside and cristobalite. After 1150degreesC, the most important change in the fired bodies was the complete reaction of the quartz. Paralleling the disappearance of quartz and gehlenite, the anorthite, diopside and cristobalite phases occured in the fired body.