Fig. 9

General morphological view of the six samples (NT1-NT6). In NT1 to NT4, the halite (light gray) and Ca and K sulfates (dark grey) crusts are shown, with some calcium-phosphate crystals (in white) and black organic particles. NT5 shows a crust composed mainly of layered and mesostructured gypsum with traces of Na and Cl (halite) and sulfates. In NT6, there is a pore with a quartz grain with signs of corrosion and a film with acicular-planar halite crystals, and a matrix composed of calcite and a mixture of calcium silicates, halite, sulfates, and calcium-phosphate. Hl (halite); Gp (gypsum); Anh (anhydrite); Brt (brushite); Qz (quartz); Hbe (humberstonite); Ugm (ungemachite). Minerals symbols after [44] except for Brt (brushite)