Figure 2.

SEM images of CaCO₃ precipitates in the Crystal Hotel. a, b) Amorphous calcium carbonate obtained at [Ca²⁺]=2.5 mm and [Mg²⁺]=1.25 mm. Further images of ACC precipitated under a range of solution conditions are shown in Figures S3 and S4. c, d) Calcite crystals grown without additives at [Ca²⁺]=5 mm and [Ca²⁺]=50 mm, respectively. The purple dotted line indicates the boundaries of the individual “room”. The insets show crystals at higher magnifications. e–h) Crystals formed the presence of e) [Ca²⁺]=2.5 mm and [Mg²⁺]=1.25 mm, f) [Ca²⁺]=2.5 mm and [PSS]=500 μg mL⁻¹, g) [Ca²⁺]=2.5 mm and [PSS]=250 μg mL⁻¹, and h) [Ca²⁺]=1.25 mm and [PSS]=250 μg mL⁻¹.