TEM STUDY OF SYNTHETIC HILLEBRANDITE (CA2SIO4.H2O)

Hillebrandite (dicalcium silicate hydrate) was produced by a hydrother mal process. Its crystal structure and microstructures were investigat ed by conventional TEM and HREM. Most hillebrandite fibers showed thei r elongation to be parallel to the b axis and tended to lie on the {00 1} cleavage planes. Selected area diffraction patterns frequently disp layed continuous streaking, and corresponding dark-field images reveal ed stacking disorders perpendicular to the fiber axis. The morphology, stacking disorders, and extinction conditions of {hk0} reflections an d hillebrandite resembled those of the minerals wollastonite (CaSiO3) and pectolite (Ca2NaH[SiO3]3). Periodic (100) faulting with a displace ment vector 1/2 b is suggested to be the major origin of the streaking and the systematic absences in hillebrandite.