Figure 3

(a) Detail of a BGS bouquet: Hybrid speleothems (detail 2) formed between acicular speleothems (detail 1) and tubular speleothems (detail 3). (b) Photomicrograph under cross polarized light of the longitudinal section of an acicular speleothem, which is made of crystals growing in optical continuity (CAC). (c) Mineralogy of acicular speleothems was investigated with X-ray diffraction showing that these speleothems are made of aragonite. The black spectrogram is the analysis, which is compared to the aragonite XRD peaks. (d) SEM image of an acicular speleothem whose composition is indicated by the EDX analysis reported in panel (e) upper curve. (f) Photomicrograph under cross polarized light of the transverse section of a hybrid speleothem. The center and the rim have morphologies similar to those of acicular and tubular speleothems, respectively. (g) Photomicrograph under cross polarized light of the transverse section of a tubular speleothem, which is made of crystals growing in non-optical continuity. (h) Mineralogy of tubular speleothems was investigated by means of X-ray diffraction showing that these speleothems are made of calcite. The black spectrogram is the analysis, which is compared to the calcite XRD peaks. i) SEM image of the outer wall of a tubular speleothem which is covered by a biofilm (Fig. 2). i) EDX analysis performed on the outer wall of a tubular speleothem indicating that the biofilm is mainly made of C. However, as the EDX analysis penetrates few micrometers the surface the Ca and O peaks suggest that the first layer covering the wall is made of a carbonate mixed with organic matter (Fig. 2). Photos by: Nicola Tisato, Francesco Sauro and Tomaso R. R. Bontognali.