Abstract—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°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°C for 72 h and by cooling of the melt from 830 to 650°C for 30 min. The obtained carbonates were studied by Raman spectroscopy. The Raman spectrum of bütschliite is characterized by the intense band at 1093 cm–1 and several bands at 1402, 883, 826, 640, 694, 225, 167 and 68 сm–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 сm–1. In the Raman spectrum of K2Ca2(СO3)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 сm–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.