An unusual carbonate mineral, huntite (Mg 3 Ca(CO 3 ) 4 ), is present in Upper Neogene lacustrine formations of the Kozani Basin, Northern Greece. This carbonate, either pure or mixed with variable proportions of hydromagnesite and magnesite, forms extensive deposits that accumulated in ponds on a lake-margin carbonate flat. Although labile and metastable, huntite also is the main detrital component of fluvial-dominated delta sequences in some parts of the basin. Clastic huntite is present mainly in foresets, trough cross-stratified units, and channel forms in terrigenous lithofacies towards the basal part of deltaic assemblages. Detachment of fragments from cohesive huntite pond deposits may have been favored by expansion through wetting rather than by desiccation and further contraction of the chemical sediment. This first documented occurrence of clastic huntite places some uncertainties on the presumed chemical and mechanical instability of huntite under natural conditions.

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