A member of a chemically diverse, structurally related group of minerals that comprise substantial fractions of both the Earth's crust and upper mantle. The term was coined by Albert Johannsen in 1911; it is a contraction of biotite (a mica), pyroxene, and amphibole.
The pyroxene minerals contain single chains of corner-sharing silicate (SiO4) tetrahedra, and the amphiboles contain double chains. Likewise, the micas and other related biopyriboles (talc, pyrophyllite, and the brittle micas) contain two-dimensionally infinite silicate sheets, which result in their characteristic sheetlike physical properties. In the pyroxenes and amphiboles, the silicate chains are articulated to strips of octahedrally coordinated cations, such as magnesium and iron; and in the sheet biopyriboles, the silicate sheets are connected by two-dimensional sheets of such cations. In addition to the classical single-chain, double-chain, and sheet biopyriboles, several biopyriboles that contain triple silicate chains have been discovered. See also Biotite; Mica; Pyroxene; Silicate minerals.
Pyroxenes, amphiboles, and micas of various compositions can occur in igneous, metamorphic, and sedimentary rocks. Pyroxenes are the second most abundant minerals in the Earth's crust (after feldspars) and in the upper mantle (after olivine). Unlike the pyroxenes, amphiboles, and micas, the wide-chain biopyriboles do not occur as abundant minerals in a wide variety of rock types. However, some of them may be widespread in nature as components of fine-grain alteration products of pyroxenes and amphiboles and as isolated lamellae in other biopyriboles. See also Igneous rocks; Metamorphic rocks; Sedimentary rocks. —This unsigned comment was added by 188.8.131.52 (talk).