Characteristic structure of Cl-amphibole is reviewed, and its application to chemical zoned amphibole from the Ramnes cauldron is summarized.Large ionic radius of Cl- brings geometrical and chemical effects to the amphibole structure. In the Cl-amphibole, the double chain is significantly deformed to fit expanded octahedral strips, which is achieved by substitution of ~(IV)Al for Si (geometrical constraint). The Cl- projects toward the A site and there is a interaction between Cl- and cations in the A site (A site constraint). The short range order of Fe~(2+)-Cl- is observed in Cl-amphibole (chemical constraint). These constraints simultaneously control the Cl- content in amphibole and imply that Cl- substitutes for OH- only in the ferro-paragasite or ferro-hastingsite component.Based on these structural considerations on Cl-amphibole, Cl- variations in the zoned amphibole from the Ramnes cauldron were interpreted. The zoning were developed under different fluid conditions in chemistry and temperature.
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