Fire clay of the Kabutarkuh deposit, located about 50 km southeast of Gonabad (Khorasan Province), was analyzed for its mineralogical and chemical compositions. Kaolinite, pyrophilite, quartz, dickite, gypsum, illite and alunite are the dominant minerals, and a minor phase of hematite is also present. Geochemical data show that the whole rock sample is mainly composed of SiO₂, Al₂O₃ and K₂O. Chemical results and petrographical studies give an indication of andesite-latite parent rock, which has been altered under the influence of hydrothermal fluids. The chondrite-normalized rare earth element (REE) patterns show enrichment in the Light REEs. The LREE/HREE ratio of upper layer is higher than the lower ones, which indicates mobility of HREE toward the depth. Generally, REE, trace elements and major elements patterns show evidence of intense alteration and weathering processes related to kaolinization. The high measured values of EC and Low measured values of PH are due to solubility of alunite and gypsum minerals.