Hundred-micrometer-sized calcium-aluminum-silicates (CAS) inclusions occur in moissanite-4 H , moissanite-15 R , and moissanite-6 H from Turkey. These inclusions commonly consist of tabular exsolution lamellae of two different minerals. By combined electron microprobe and Raman spectroscopy analysis, at least eight different, essentially Mg- and Fe-free Ca-Al-silicate or Al-silicate phases have been discerned. The most common phase is dmisteinbergite, a hexagonal modification of CaAl 2 Si 2 O 8 , occurring in association with lamellae of Ca x (Al,Si) 1−x O 3 or Ca 1−x (Al,Si) 2+x O 5 compositions. All three phases contain significant amounts of BaO (up to 2 mol% of celsiane component in dmisteinbergite), SrO, SO 3 , and light rare earth elements (LREE). In particular, Ca 1−x (Al,Si) 2+x O 5 contains up to 2.1 wt% of LREE, 3.9 wt% of F, and significant traces of Cl, while it is also associated to osbornite (TiN). Pure ghelenite, Ca 2 Al 2 SiO 7 , and three additional compositions, namely CaAl 4–x Si x O 7 , Ca 1–x (Al,Si) 3+x O 6 , and Ca 3–x (Al,Si) 6+x O 14 have been found, either occurring as single grains or forming exsolution lamellae. They also contain significant amounts of BaO, SrO, SO 3 , and LREE. One last intriguing phase is composed in average of 65.9 wt% SiO 2 , 17.4% Al 2 O 3 , 3.0% alkalis, 6.0% BaO, 2.0% CaO+MgO, 0.9% ZrO 2 , and up to 0.5% LREE. Dmisteinbergite and ghelenite show Raman peaks in very good agreement with literature data, Ca x (Al,Si) 1–x O 3 shows main Raman modes at 416 and 1009 cm −1 , Ca 1–x (Al,Si) 3+x O 6 at 531 and 1579 cm −1 while Ca 3–x (Al,Si) 6+x O 14 has a strong peak at 553 cm −1 . CaAl 4–x Si x O 7 shows a weak Raman pattern, while Ca 1–x (Al,Si) 2+x O 5 has no detectable Raman modes. Since the association moissanite-CAS is thermodynamically not stable at ambient pressure and moissanite crystals hosting the CAS phases have δ 13 C values typical of deep-mantle origin, we interpret the CAS inclusions as partially retrogressed HP minerals. Striking analogies exist between observed CAS compositions and experimentally obtained HP-HT mineralogy. For instance, Ca x (Al,Si) 1–x O 3 contains up to 25 mol% of Al 2 O 3 , which is considered as the upper limit of alumina solubility in Ca-perovskite. The study confirms that CAS phases are an important mantle depository for large ion lithophile elements (LILE) and LREE.