when calcium and bicarbonate ions were mixed at room temperature ( approximately 20 degrees c ) to give concentrations of 4 mmol/1 and 21 mmol/1 respectively and the ph of the solution was kept at 8.3 , vaterite , a form of calcium carbonate , was precipitated almost immediately as spheres of diameter 45 micron .
C0006675
calcium
C0006681
calcium carbonate