Abstract: The trona-bearing serie of the "Hırka Formation" of Miocene age in the Beypazarı (Ankara) basin havebeen examined by optical and X ray diffraction techniques.In addition to trona, trona-bearing serie consist mainly of pirssonite, nahcolite, dolomite, calcite, magnesite, clinoptilolite, analcime, K-feldspar, quartz, smectite, illite, pyrite, biotite and hornblende. Studies shown that, tronabearing zones (lower and uper trona horizons) are composed of mainly of 85 % well crystallized natural soda mineralssuch as trona, pirssonite, nahcolite and 15 % dolomite. Dolomites in the non trona bearing zones are of Ca-Dolomitestypes. On the other hand, the ideal crystallographic structure of dolomites have been determined in the lower and uppertrona horizons.