pyroksen

Pyroksen is a term used in several languages for the pyroxene group of minerals, a major class of inosilicates that form single chains of silicon-oxygen tetrahedra. Pyroxenes are common rock-forming minerals in both igneous and metamorphic rocks. They exhibit extensive solid-solution among members, with composition forming continuous series between end-members.

Structure and composition: The typical pyroxene structure consists of single chains of SiO4 tetrahedra that share two oxygens with neighboring tetrahedra, creating SiO3 chains. The general chemical formula is XY(Si,Al)2O6, where X and Y are metal cations such as Ca, Na, Mg, Fe2+, Fe3+, Mn, and Al can substitute for silicon in the framework. Pyroxenes are divided into orthopyroxenes (orthorhombic symmetry) and clinopyroxenes (monoclinic symmetry), differing primarily in crystal structure and reflection planes.

Physical properties: Pyroxenes are usually hard and moderately dense, with a vitreous to submetallic luster. They commonly display two cleavage directions at about 90 degrees. Colors range from colorless and pale to green, brown, or black, depending on chemical composition. Hardness on the Mohs scale is typically in the range of 5 to 7.

Occurrence and varieties: Orthopyroxenes include enstatite and ferrosilite; clinopyroxenes include diopside, augite, and hedenbergite, among others. Jadeite is a well-known clinopyroxene variety. Pyroxenes are abundant in basalt, gabbro, peridotite, and many metamorphic rocks formed at high temperatures and pressures.

Significance: As a major group of rock-forming minerals, pyroxenes provide key clues about the temperature, pressure, and chemical conditions during rock formation and metamorphism, and they are important in petrographic classification and petrology.

---