Microbial biscuits of vaterite (a polymorph of CaCO3) were found in Lake Issyk-Kul, Republic of Kyrgyzstan. Four sections were defined from the inner part to the outer part of these microbial biscuits: (1) a nucleus made up of coated discrete bacterial forms, (2) a massive coating attributed to the calcification of the mucilaginous sheath of the bacterial community, (3) a thick lamina composed of large fibers of vaterite, and (4) a discontinuous external coating incorporating foreign elements such as diatoms. The origin of these microbial biscuits is attributed to bacterial activity. The vaterite formation seems to be related to the hexagonal structure of the mucilaginous sheath and to the inhibitor role of the phosphorous present in the water during calcite precipitation.

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