Abstract
This paper reviews current status on the crystal chemistry of the calcic amphiboles. Calcic amphiboles show a wide range in chemistry, and also have several crystallographically unique sites in the crystal structure. Consequently, our understanding on the crystal chemistry of the calcic amphiboles, especially hornblendes, has not progressed quite as rapidly as for the less complex silicate minerals. From 1960's to 1980's, the structure refinements of several calcic amphiboles were carried out, and cation distribution in the cation sites were discussed. As a result of the above investigations, cation distribution in hornblendes has beenrevealed. Namely, Al tends to occupy the T(1) site in preference to T(2) site inthe hornblende containing 0.5-2.0 pfu ofiv Al. In the metamorphic hornblendes, Al, Fe3+ and Ti occupy only the M(2) site, and Mg prefers the M(2) site to the M(1) and M(3) sites. On the other hand, the volcanic hornblendes indicate a more disordered cation distribution among the M(1), M(2) and M(3) sites than the metamorphic hornblendes.
