In a calcareous sinter precipitated from cold saline spring water at Shiowakka, Hokkaido, Japan, ikaite (CaCO₃·6H₂O) was found in winter, subsequent to the finding of monohydrocalcite with calcite in the previous summer. The formation of the ikaite was favored by low temperature, while that of the monohydrocalcite was favored by green algae inhabiting the interface of water and air (Ito, 1993). Ikaite precipitates in weak flows, forming rimstone and encrustation embedded in ice. The idiomorphs of ikaite are dissimilar to glendonite-type calcite pseudomorphs, but the pointed termination of the calcite pseudomorphs can be accounted for the combination of planes of ikaite crystals observed by scanning electron microscope.