HYDROXYLELLESTADITE FROM THE GARNET-WOLLASTONITE SKARNS OF ARIMAO-NORTE (CUBA)

摘要

Ellestadite- the rare mineral of apatite group- has been found out for the first time at Cuba, in Arimao-Norte skarn deposit. Ellestadite associates there with wollastonite, garnet of grossular-andradite composition, diopside, vesuvian, calcite, xonotlite, pyrite, etc. It forms small segregations and widespread in disseminated grain. Several its large localitites have been revealed by the drill hole PBW-19, where some intervals of the corp, up to several metres in length, were represented by the ellestaditic rock containing 97-99 percent of this mineral, with minor admixtures of garnet, pyrite, magnetite and stilpnomelane. Density 3.020 g/cm~3, microhardness 390 kg/mm~2 (4.5 on Mohs), indices of refraction No=1.651+0.002, Ne=0.647+0.002. The paper displays data on thermographic and IR spectroscopy peculiarities of the mineral, their interpretation is given also. Chemical composition of ellestadite corresponds to the formula: (Ca_(9.99)Na_(0.001))_(10)((SiO_4)_(2.955)(CO_3)_(0.088)(PO_4)_(0.003))_6 X ((OH)_(1.19)O_(0.49)Cl_(0.31)F_(0.03)_(2.02). Obtained data confirm the typical feature of ellestadite-the Si:S ratio in tetrahedral positions is quite close to 1:1. Unit cell parameters: a=9.526, b=9.506, c=6.922 A, #gamma#=119.99 deg, V=542.89 A~3.