Fig. 2

Scanning electron microscope (SEM) images of cyanobacterial Lyngbya filaments and energy spectrum charts of carbonates, with green alga filaments (diameter < 10 μm); the same samples as of Fig. 1. Diameters are marked by red circles/dots. a Four filaments with scattered carbonate grains on their surfaces; b Enlargement of the red box in a; +: positions of energy spectrum tests; c Three filaments covered by carbonate grains; d Enlargement of the red box in c; e Carbonate grains on the surface of a filament; f Enlargement of the red box in e, showing carbonate grains consisting of rod-shaped crystals which are 0.1 × 1 μm² in size; g, h Energy spectrum charts of the positions 14 and 15 in b