Abstract: Economically important borate deposits were formed as chemical precipitates in lacustrine environments.Factors controlling the formation of these deposits are mainly the composition, pH and the temperature of motherliquors.Experimental studies and field observations show that Turkish borate deposits can conveniently be divided in twogroups; a-those which have shown a complete sequence of precipitation in a Na;2O-CaO-B2O3-H.2O system (Kırkatype), and b-aJl other known deposits that do not contain Na borate.Deposits of group (a) were most likely formed from a solution having NaoO7CaO ratio close to unity and above,provided that the solution contains the necessary B concentration. The result of precipitation from such a solution would give a vertical sequence of Ca, Na-Ca and Na borate layers which indicates gradual increase in concentration within the lakesystem. The lateral variation in such a deposit is that Na-borates are dominant at the central and deepest parts of thedeposit. These Na-borate layers are progressively transformed in Na-Ca and Ca-borates towards the edge of thebasin.