Crystal structures and cation occupancies have been refined using single-crystal X-ray diffraction data for natural specimens of (1) manganoan, intermediate, and calcian bus-tamites; (2) ferroan and manganoan wollastonites; and (3) serandite and manganoan pecto-lites (schizolite). Although the silicate chains of three-tetrahedral repeat are similar in these minerals, the differences in cation arrangements in the octahedral layers result in three structures with distinct stacking schemes of tetrahedral and octahedral layers. The unchanged occupancies in the М3 and M4 sites of bustamite, M3 site of wollastonite, and Na site of pectolite are important for determination of the structure types, whereas the stepwise substitutions in M1 and М2 explain the observed compositional variations in bustamite and pectolite.

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