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The Sambhar Lake playa sediments in Thar desert, western India, host a variety of evaporite minerals. Carbonates form a major proportion of the evaporites in a 23 m deep core and several dolomite-rich horizons are recorded. Our XRD and DTA based investigations show that these dolomites are non-stoichiometric and disordered (proto-dolomites) except at one level (4.08 m) from where a well-ordered dolomite is reported. We also record frequent variation in the characteristics of dolomites with depth in terms of structural ordering, Ca/Mg ratio and Fe content. Dolomites reported form the Sambhar Lake playa are interpreted to be authigenic due to the absence of any carbonate rock in the catchment and seem to be derived from a precursor calcite under (sub-) evaporitic conditions.