BUSTAMITE with APOPHILLITE, South Mine, BROKEN HILL, NSW, AUSTRALIA (miniature)

Bustamite is a rare mineral, a type of calcium manganese inosilicate, which belongs to the wollastonite group. Common impurities like magnesium, zinc, and iron can replace manganese in its structure. It is the high-temperature form of CaMnSi2O6, while johannsenite represents the low-temperature form. The transition between these two occurs at 830 °C (1,530 °F), although this process can be quite slow.

Bustamite might be mistaken for light-colored rhodonite or pyroxmangite, but unlike these two minerals, which are biaxial (+), bustamite is also biaxial.