Infrared and Raman spectroscopic characterization of the silicate-carbonate mineral carletonite - KNa_4Ca_4Si_8O _(18)(CO_3)_4(OH,F)·H_2O

摘要

An assessment of the molecular structure of carletonite a rare phyllosilicate mineral with general chemical formula given as KNa _4Ca_4Si_8O_(18)(CO_3) _4(OH,F)·H_2O has been undertaken using vibrational spectroscopy. Carletonite has a complex layered structure. Within one period of c, it contains a silicate layer of composition NaKSi_8O _(18)·H_2O, a carbonate layer of composition NaCO _3·0.5H_2O and two carbonate layers of composition NaCa_2CO_3(F,OH)_(0.5). Raman bands are observed at 1066, 1075 and 1086 cm~(-1). Whether these bands are due to the CO32- ν_1 symmetric stretching mode or to an SiO stretching vibration is open to question. Multiple bands are observed in the 300-800 cm~(-1) spectral region, making the attribution of these bands difficult. Multiple water stretching and bending modes are observed showing that there is much variation in hydrogen bonding between water and the silicate and carbonate surfaces.