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| Orthopyroxene | |
|---|---|
| Name | Orthopyroxene |
| Category | Pyroxene group |
| Formula | (Mg,Fe)SiO3 |
| Crystal system | Orthorhombic |
| Color | Green, brown, black |
| Cleavage | Two at ~90° |
| Hardness | 5–6 |
| Luster | Vitreous to pearly |
| Streak | White to gray |
| Gravity | 3.2–3.8 |
Orthopyroxene Orthopyroxene is a common rock-forming silicate mineral in the pyroxene group found in igneous and metamorphic rocks. It occurs in mafic and ultramafic terrains associated with plutonic bodies, ophiolites, and high-grade metamorphic terranes, and it plays a central role in interpreting tectonic processes and mantle chemistry. Major studies of orthopyroxene feature in petrology research from the Geological Society of America to the Smithsonian Institution and have informed investigations by institutions such as Caltech and the Max Planck Society.
Orthopyroxene is a chain silicate mineral that forms a solid solution between magnesium-rich and iron-rich endmembers, historically investigated by researchers at the University of Cambridge, Harvard University, and the University of Oxford. Key field localities include the Bushveld Complex, the Sierra Nevada, the Icelandic ophiolites, and the Himalayas, with analytical work published in journals by the American Geophysical Union and the European Geosciences Union. Classic petrological textbooks from authors associated with MIT and UCL discuss orthopyroxene’s role in magmatic differentiation and mantle peridotite studies performed by teams at Columbia University and the University of Tokyo.
Orthopyroxene’s idealized composition is (Mg,Fe)SiO3, forming a solid solution between Enstatite and Ferrosilite, with minor subsolidus components such as Manganese and Calcium substitutions noted in work at the University of Minnesota and ETH Zurich. Its orthorhombic crystal structure was elucidated using techniques developed at Bell Labs and refined via single-crystal diffraction at facilities like the European Synchrotron Radiation Facility and Argonne National Laboratory. Structural investigations reference symmetry operations catalogued by the International Union of Crystallography and experimental constraints from high-pressure apparatus at Carnegie Institution for Science and Lawrence Livermore National Laboratory. Studies by researchers affiliated with the University of California, Berkeley and Pennsylvania State University document chain silicate linkage and octahedral site occupancy relevant to trace element partitioning explored by teams at the Woods Hole Oceanographic Institution.
Orthopyroxene exhibits characteristic optical properties described in manuals used by the US Geological Survey, with birefringence, pleochroism, and extinction angles analyzed in labs at Stanford University and the Rockefeller University. Its physical parameters—hardness, specific gravity, cleavage—are measured in collections at the Natural History Museum, London and the American Museum of Natural History. Microprobe and Raman spectroscopy work from groups at Oak Ridge National Laboratory and McGill University quantify compositional zoning and OH-defects, while transmission electron microscopy studies by teams at IBM Research and Rutherford Appleton Laboratory reveal dislocation structures important to deformation studies cited by the USGS and the Geological Survey of Canada.
Orthopyroxene occurs in peridotites of the Kola Peninsula and chromitite-bearing intrusions such as the Bushveld Complex, and it is a principal phase in cumulate rocks examined in the Ellesmere Island field campaigns organized by the Royal Society. It crystallizes from basaltic to andesitic magmas studied by researchers at NASA and in meteorites curated by the Smithsonian Institution National Museum of Natural History. Metamorphic assemblages containing orthopyroxene are central to studies of Blueschist and Eclogite facies transitions conducted by teams at ETH Zurich and UCLA, and field mapping by the Geological Survey of Finland and Geological Survey of India documents paragenetic sequences in regional metamorphism.
Classification schemes for pyroxenes developed by committees at the International Mineralogical Association and summarized by authors at Cambridge University Press place orthopyroxene in contrast to clinopyroxene members such as Diopside and Augite. Phase equilibria and the orthopyroxene-clinopyroxene relations are explored in experimental petrology at Penn State, Lehigh University, and the University of Lisbon, with thermodynamic databases curated by the Geochemical Society and computational work from groups at Princeton University and ETH Zurich modeling solid solution and exsolution textures relevant to exsolution lamellae observed in samples from the Svalbard archipelago.
Orthopyroxene-bearing assemblages provide geothermobarometric constraints applied in studies of continental collision zones like the Alps and the Tibet plateau, with methodologies refined at University College London and Imperial College London. Isopleth and exchange geothermometers using orthopyroxene and garnet pairs were calibrated in experiments at Lehigh University and utilized in tectonometamorphic reconstructions by researchers at the University of Edinburgh and the Australian National University. Thermobarometric results inform models of lithospheric processes developed by groups at Princeton, Stanford, and the Max Planck Institute for Chemistry.
Orthopyroxene-bearing rocks are associated with magmatic sulfide deposits and platinum-group element mineralization in provinces like the Bushveld Complex and Stillwater Complex, impacting exploration by companies based in South Africa and Montana. Petrological studies involving orthopyroxene guide mineral exploration programs coordinated with agencies such as the US Geological Survey and the Geological Survey of Canada, and industrial applications in ceramics and refractories have been investigated by research groups at Fraunhofer Society and NIST. Academic collaborations among institutions like Cornell University, University of Western Australia, and Tohoku University continue to explore orthopyroxene’s role in mantle metasomatism and ore genesis.
Category:Pyroxene group minerals