In geology and mineralogy, a mineral group is a set of mineral species with essentially the same crystal structure and composed of chemically similar elements.[1]
For example, the amphibole group consists of 15 or more mineral species, most of them with the general unit formula, where A is a trivalent cation such as or, B is a divalent cation such as,, or, and C is an alkali metal cation such as,, or . In all these minerals, the anions consist mainly of groups of four tetrahedra connected by shared oxygen corners so as to form a double chain of fused six-member rings. In some of the species, aluminum may replace some silicon atoms in the backbone, with extra B or C cations to balance the charges.