Low-Mg calcite precipitates more or less constantly during all seasons within the active depositional zone. This extends for a few hundred microns upon the external surface of the deposits, where the biofilm occurs. The latter is composed of a heterogeneous community of green algae, filamentous cyanobacteria and other types of prokaryotes, Actinobacteria and fungi, with a variable amount of extracellular polymeric substances (EPS). Porous micro-columns (50 to 150 渭m in size), separated by interstitial spaces, characterize the active depositional zone. Here precipitation always begins with organomineral nanospheres (10 to 20 nm diameter), both along the external surfaces and within internal cavities of the micro-columns, by replacing degraded organic matter, and at point-sites suspended within living cyanobacterial tufts along the external surface of their sheaths, indicating that the biological activities of the biofilm are crucial, with its living organisms and non-living organic matter.
Organomineral nanospheres successively agglutinate to form irregular to rod-shaped crystal aggregates, 100-200 nm in size, that with their further agglutination create two basic types of larger, more ordered, crystal structure: polyhedrons in the range of 1-2 渭m, and minute triads of calcite fibres varying in length from ~ 0.4 (short triads) to ~ 1 渭m (long triads). Basic crystal structures coalesce to form larger crystals (mainly tetrahedrons tens of microns in size) that constitute the micro-columns.