Natural 1.1 and 1.4 nm tobermorites from Fuka, Okayama, Japan Chemical analysis, cell dimensions, 29Si NMR and thermal behavior

A natural specimen of tobermorite, which contained both 1.1 and 1.4 nm phases, was studied by optical microscopy, X-ray powder diffractometry (XRD), EPMA, analytical TEM, 29Si NMR and TG-DTA, and the results were compared with those for a specimen from Crestmore, California. The sample, occurring as a vein in contact with metamorphic rocks, could be divided into three zones. In two of the zones containing only the 1.1 nm phase, about 10% of the Si were substituted by Al. The third zone was an intergrowth of 1.1 and 1.4 nm tobermorites and contained almost no Al. The basal spacings of the 1.1 and 1.4 nm tobermorites were changed mainly to 0.9 nm by heating at 300 deg. C for 24 h but in some parts remained at 1.1 nm. 29Si NMR results showed that silicate anions in the 1.1 nm tobermorite were double chains, which changed mainly into single chains, on heating at 300 deg. C. XRD results indicated that natural tobermorites are more highly crystalline than the synthetic ones of calcium silicate products