Microbial biscuits of vaterite in Lake Issyk-Kul (Republic of Kyrgyzstan)

Microbial biscuits of vaterite (a polymorph of CaCO3) were found in Lake Is syk-Kul, Republic of Kyrgyzstan. Pour sections were defined from the inner part to the outer part of these microbial biscuits: ii) a nucleus made up o f 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 vater ite formation seems to be related to the hexagonal structure of the mucilag inous sheath and to the inhibitor role of the phosphorous present in the wa ter during calcite precipitation.