Al成分に富む天然産および合成電気石の鉱物学的性質

抄録

Chemical and X-ray studies have been made of Al-rich tourmalines from the Kano mine, Miyazaki Prefecture, from granitic and pegmatitic rocks in Kyushu, and synthetic materials prepared hydrothermally in the temperature and pressure ranges 500-700°C and 1, 000-2, 000 bars. In these synthetic works oxide mixtures with compositions ranging from Al-rich Mg-tourmaline to Al-rich Fe²⁺-tourmaline were used. The analytical results show that the sum of divalent cations in the Al-rich tourmaline is always less than 3.0, and univalent cations less than 1.0, and that the amount of alkali (principally Na) decreases with increasing Al content in Y position of the general formula, XY₃Z₆B₃Si₆O₂₇ (OH)_4', and the amount of [Na+(OH)] decreses with increasing [R³+(in Y)-R³+(in Si position)] value. The cell parameters of Al-rich tourmaline are slightly smaller than those of tourmaline with completely occupied by Mg and/or Fe²⁺ ions in Y position, and show a progressive decrease and have a tendency to approach to those values of alkali-free tourmaline (Rosenberg, 1975) or buergerite from those of dravite or schörl, with increasing Al content in Y position.