Synthesis and Raman Spectra of K-Ca Double Carbonates: K2Ca(CO3)2 Butschliite, Fairchildite, and K2Ca2(CO3)3 at 1 Atm

This paper reports the synthesis of double K-Ca carbonates at atmospheric pressure in closed graphite capsules. The mixtures of K2CO3 and CaCO3 corresponding to the stoichiometry K2Ca(CO3)(2) and K2Ca2(CO3)(3) were used as starting materials. The low-temperature modification of K2Ca(CO3)(2) was synthesized by a solid-state reaction at 500 degrees C during 96 h. The high-temperature modification of K2Ca(CO3)(2) as well as K2Ca2(CO3)(3) were synthesized by a solid-state reaction at 600 degrees C for 72 h and by cooling of the melt from 830 to 650 degrees C for 30 min. The obtained carbonates were studied by Raman spectroscopy. The Raman spectrum of butschliite is characterized by the intense band at 1093 cm(-1) and several bands at 1402, 883, 826, 640, 694, 225, 167 and 68 cm(-1). The Raman spectrum of fairchildite has characteristic intense bands at 1077 and 1063 cm(-1), and several bands at 1760, 1739, 719, 704, 167, and 100 cm(-1). In the Raman spectrum of K2Ca2(CO3)(3), the intense lines were found at 1078 and 1076 cm(-1) and several lines at 1765, 1763, 1487, 1470, 1455, 1435, 1402, 711, 705, 234, 221, 167, 125 and 101 cm(-1). The collected Raman spectra can be used to identify carbonate phases entrapped as microinclusions in phenocrysts and xenoliths from kimberlites and other alkaline rocks.