LIVING HYDROMAGNESITE STROMATOLITES FROM TURKEY

Salda Golu (Lake), in southern Turkey, is a highly alkaline (pH > 9) f reshwater lake in which composite stromatolites several metres high ar e formed by microbially induced precipitation of hydromagnesite. The m agnesium and carbonate in the lake waters were dissolved during passag e through ultramafic rocks. Precipitation is brought about by the flor a of diatoms and cyanobacteria forming the surface of the stromatolite s, but does not occur in direct contact with cells. Stromatolites have previously been reported from environments ranging from fully marine through brackish water to a variety of freshwater lacustrine and fluvi al situations. The principal importance of these structures lies in th eir novel mineralogy. Hydromagnesite Mg4(OH)2(CO3)3 . 3H2O is commonly regarded as a low-temperature hydrothermal mineral.