Abstract

The hypothesis that the formation of tubular crystals of chrysotile is the result of misfit of the alternate brucite and silica layers, is tested by means of chemical substitution. Increasing the size of the tetrahedral layer by substituting Ge4+ for Si4+ results in the formation of hexagonal platy crystals of the serpentine phase, Mg6Ge4O10(OH)4. Decreasing the size of the octahedral layer and at the same time increasing the size of the tetrahedral layer is accomplished by partial substitution of Al3+ into the structure to form platy aluminian serpentine, Mg5AlAlSi3O10(OH)4. The replacement of Mg2+ by the similar-sized Ni2+ ion yields a serpentine Ni6Si4O10(OH)4 which is either tubular or platy, depending on other factors. Another serpentine phase synthesized, Ni6Ge4O10(OH)4, forms hexagonal platy crystals. Other substitutions using the following ions: Mn2+, Zn2+, Co2+, Fe3+, Cr3+, and Ga3+, fail to yield a serpentine type structure.

A number of other hydrosilicate type structures have been synthesized, and comparisons are made of the phase equilibrium relations determined to be present among phases in the systems, MgO-SiO2-H2O, NiO-SiO2-H2O and MgO-GeO2-H2O.

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