Abstract
At Shiowakka calcareous sinter dome, rare calcium carbonate minerals such as vaterite, monohydrocalcite and ikaite precipitate from cold spring water. Calcite is main precipitates in those minerals without in winter.
By the laboratory work in a cold chamber, the precipitation of ikaite from Shiowakka spring water at about 6 degrees C. water temperature was observed. Ikaite precipitate easily from melting water of ice formed by the spring water. Those crystals of ikaite floated on the surface of cold spring water in a beaker. Calcite precipitation following after that of ikaite and calcite aggregation showed just likes fractal texture. The order of crystallization from ikaite to calcite was common in the synthetic experiments and almost all calcite appeared following ikaite.
The inhibitor of calcite nucleation such as phosphates ions has been discussed for the formation of natural ikaite in previous papers. But, the contents of PO4 ions in the Shiowakka water are the smallest in the natural water chemistry from which ikaite precipitated.
From observation of ikaite precipitation in a room and the field, it is supposed that natural dissolved organic matter is useful factor for the formation of ikaite from the cold spring water at low water temperature. That matter may effect on the inhibitation of calcite formation.
