Bustamite is a calcium manganese inosilicate (chain silicate) and a member of the wollastonite group. Magnesium, zinc and iron are common impurities substituting for manganese. It is a polymorph of johannsenite, with bustamite as the high-temperature form of CaMnSi₂O₆ and johannsenite as the low temperature form. The inversion takes place at 830 °C, but may be very slow. Bustamite could be confused with light-colored rhodonite or pyroxmangite, but both these minerals are biaxial (+) whereas bustamite is biaxial (-).