Pyroxenoids

Single-chain silicates like pyroxeneA class of silicate (SiO3) minerals that form a solid solution between iron and magnesium and can contain up to 50% calcium. Pyroxenes are important rock forming minerals and critical to understanding igneous processes. For more detailed information, please read the Pyroxene Group article found in the Meteoritics & Classification category., but the tetrahedra composing chains are rotated and twisted. Octahedrally coordinated cations occur between chains as in pyroxenes. The interval of repetition is different for each pyroxenoid (below). The twisting results in lower symmetryProperty of an object if some spatial manipulation of it results in an indistinguishable object. A symmetric object can be superimposed on itself by some operation. than pyroxenes (all pyroxenoids are triclinic) and a splintery cleavage and sometimes fibrous habit.

The most common pyroxenoid is wollastonite (CaSiO3), which has Ca²⁺ in irregular octahedral coordination linking the chains. It is common in metamorphosed limestones. Other pyroxenoids include bustamite, (Mn,Ca,Fe)SiO₃, with a repeat of ~14 Å, rhodonite, MnSiO₃, with a repeat of 12.5 Å, and pyroxmangite, (Mn,Fe)SiO₃, with a repeat of ~17 Å. There is significant chemical variation and solid solutionCompositional variation resulting from the substitution of one ion or ionic compound for another ion or ionic compound in an isostructural material. This results in a mineral structure with specific atomic sites occupied by two or more ions or ionic groups in variable proportions. Solid solutions can be complete (with in the pyroxenoids, except for wollastonite, which is usually very close to pure in composition.