Fig. 6

Crystals on the filters from the experiments with ultra-pure water at \({T} = 45\), 60, 80, and \(110\,^{\circ }\hbox {C}\). Pictures show trigonal rhombohedral calcite crystals as dominating calcium carbonate polymorph: mostly as aggregates (45–\(80\,^{\circ }\hbox {C}\)) with irregular ion emplacement on the surface. The big crystal at \(110\,^{\circ }\hbox {C}\) shows some microporosity from the front view