The crystal chemistry of the amphiboles

Abstract

The major differences in unit-cell shape of the different amphibole varieties, and the respective composition ranges of the orthorhombic and monoclinic amphiboles, are related to the effects of the ionic radius of the ions occupying two of the sets of ionic sites in the structure.These are the ions which serve to link together the talc-like strips from which the structure may be regarded as being built.The reason for the existence of both limited and unlimited isomorphous substitution ranges for the same ions in different parts of the composition field is shown to depend on the different effects on chain packing of the radius of the ions occupying these two sites as compared with each other and with the sites which are wholly inside the talc-like strips.