Optical determination of water content in spherulitic vaterite

From measured indices of refraction for vaterite crystals [n, 1.650, n,o 1.550; Johnston, Merwin & Williamson, Amer.J. Sci.41,473 (1916)] and for vaterite fibers [He 1"625, no 1"538; Meyer, Z. Kristallogr.. 121,220(1965)], Wiener's formulae give two independent values for the interstitial water content of the fibers (5.9, 5.8 vol.~).The lowering of the density from 1.645 (crystal) to 1.54 (fiber) indicates 6.4 vol.% water.The decomposition product of CaCO3.6H20described by Johnston et al. can now be identified as fibrous aggregates of vaterite and water.