Relation between Chemical Compositions and Genesis-Occurrences of Tourmaline Group

According to the features of chemical compositions, members of isomorphic system for tourmaline group mineral in nature can be commonly divided into three series: shorlite-elbaite, shorlite-dravite and dravite-urite. The members of isomorphic system for shorlite-elbaite can be mainly found at the vein of differential granitic pegmatite. With the development of metasomatism in diagenetic process of pegmatite, it is changed from shorlite to elbaite. The members of isomorphic system of shorlite-dravite and dravite-urite are formed in desilicated granitic pegmatite, or occurred in regional metamorphic rocks in which the varieties of tourmaline depend to a large extent on the different chemical compositions of rocks before the regional metamorphism.