The pyroxenes are a group of important rock-forming inosilicate minerals found in many igneous and metamorphic rocks. They share a common structure consisting of single chains of silica tetrahedra and they crystallize in the monoclinic and orthorhombic systems. Pyroxenes have the general formula XY(Si,Al)2O6 (where X represents calcium, sodium, iron+2 and magnesium and more rarely zinc, manganese and lithium and Y represents ions of smaller size, such as chromium, aluminium, iron+3, magnesium, manganese, scandium, titanium, vanadium and even iron+2). Although aluminium substitutes extensively for silicon in silicates such as feldspars and amphiboles, the substitution occurs only to a limited extent in most pyroxenes.
Analysis of crystal formed in the molten rocks of a volcano might predict volcanic eruptions with as much as a year in advance, researchers claim. Mixing Seismology and Petrology Drawing data from the volcanic activity of Mount Helens from 1980 through 1986, geologists found that iron- and magnesium-rich crystals grow before an eruption, and by [...]