I. Dodony et Pr. Buseck, Polysomatism and modules of gehlenite composition and structure in the Hanic phase (Ca5Al6MgSiO17), PHYS CHEM M, 28(6), 2001, pp. 428-434
Discrete, well-ordered, single-phase crystals (the Hanic phase) form when p
owders the bulk composition of Ca5Al6MgSiO17 are allowed to react in the ab
sence of a melt. If, on the other hand, either the powders or crystals of C
a5Al6MgSiO17 are molten and then cooled, complex intergrowths form. These i
ntergrowths consist of modules having the composition and structure of Ca3A
l4MgO10 and gehlenite (Ca2Al2SiO7), forming a polysomatic series in which t
he modules occur in varied proportions. High-resolution transmission electr
on microscope (HRTEM) images reveal the details of these intergrowths. Mass
balance is achieved by the formation of this polysomatic series together w
ith Mg-substituted mayenite (Ca12-xMgxAl14O33). The tetrahedral sheets in g
ehlenite have close structural similarities to those of Ca5Al6O14. Based on
our HRTEM images, we hypothesize chemical substitutions between gehlenite
and Ca5Al6O14, resulting in gehlenite-like modules that are depleted in Si
and correspondingly enriched in Al and Ca.