Figure 3. Environmental scanning electron micrographs of white colonizations from Tomba della Scimmia (a–c) and from Ardales Cave (d–f).

(a) Bed formed of CaCO₃ nest-like aggregates (white arrow) with dispersed spheroidal elements (black arrows) from Tomba della Scimmia. (b) Small patches of CaCO₃ nest-like aggregates and filaments from Tomba della Scimmia. (c) Detail of spheroidal elements of CaCO₃ coated with filamentous bacteria from Tomba della Scimmia. Similar mineral and biological morphologies were observed in Ardales Cave walls and sediments colonized by Pseudonocardia⁸ as shown in d–f. (d) A bed of nest-like aggregates and spheroidal elements in Ardales Cave. (e) Small patches of CaCO₃ nest-like aggregates and filaments in Ardales Cave. (f) Spheroidal CaCO₃ coated with filaments in Ardales Cave.