Pyroxene
a name used for a group of minerals of very variable composition and origin, but all of which are referable (like the analogous group of amphiboles) to the same chemical type, under the general formula ROSIO2, where R may represent lime, magnesia, the protoxides of iron and manganese, and sometimes soda, potash, and oxide of zinc. Two or more of these bases are always present, the most frequent being lime, magnesia, and protoxide of iron, lime being always present and in a large percentage.