plagioclase

plagioclase
Name	Plagioclase
Category	Silicate mineral group
Formula	(Na,Ca)(Si,Al)4O8
Crystal system	Triclinic
Color	White, gray, blue, green, brown
Habit	Tabular crystals, twinned aggregates
Cleavage	Perfect on {001}
Hardness	6–6.5
Luster	Vitreous to pearly
Streak	White
Gravity	2.62–2.76

plagioclase is a major feldspar mineral series that forms an essential component of many igneous, metamorphic, and sedimentary rocks. A solid-solution series between sodium-rich and calcium-rich endmembers, it controls petrogenetic interpretations in studies involving plate tectonics, volcanic systems, continental crust, and planetary geology. Plagioclase is studied across institutions and locations ranging from the Smithsonian Institution to the Max Planck Institute for Chemistry, and its identification informs work at geological surveys and universities worldwide.

Description and Composition

Plagioclase occurs as a continuous solid solution between albite and anorthite, with compositions defined by mole percent anorthite ranging across samples from the United States Geological Survey and laboratories at the University of Cambridge, California Institute of Technology, Massachusetts Institute of Technology, Stanford University, University of Oxford, ETH Zurich, University of Tokyo, Seoul National University, Monash University, University of Toronto, University of British Columbia, University of California, Berkeley, Imperial College London, University of Paris, University of Chicago, Princeton University, Yale University, Columbia University, University of Melbourne, The Australian National University, University of Sydney, Peking University, Tsinghua University, National University of Singapore, University of Edinburgh, University of Copenhagen, Ludwig Maximilian University of Munich, University of Göttingen, Max Planck Institute for Geochemistry, Geological Survey of Japan, British Geological Survey, Geological Survey of Canada, Geological Survey of India, Norwegian Geological Survey, Swedish Geological Survey, Helmholtz Centre Potsdam, Institut de Physique du Globe de Paris, Rijksmuseum, Smith College, Northwestern University, University of Texas at Austin, Brown University, Duke University, University of Naples Federico II, Sapienza University of Rome, University of Barcelona, University of Lisbon, University of Vienna, University of Zurich, University of Helsinki, University of Oslo, Czech Geological Survey, Slovak Academy of Sciences, Polish Geological Institute, Hungarian Academy of Sciences, Russian Academy of Sciences, Moscow State University, St. Petersburg State University, Kazakh National University, University of Pretoria, University of Cape Town, University of Nairobi, Egyptian Geological Survey, Argentine Geological Survey, Brazilian National Observatory, Chile's Universidad de Chile, Pontifical Catholic University of Chile, University of Chile, Universidad Nacional Autónoma de México, Monterrey Institute of Technology.

Crystal Structure and Properties

Plagioclase crystallizes in the triclinic system with characteristic albite and pericline law twinning, studied in contexts ranging from the Royal Society meetings to conferences at the American Geophysical Union, European Geosciences Union, International Mineralogical Association, Goldschmidt Conference, GSA, AGU, and IUGS. Its framework of linked tetrahedra is documented in structural determinations at the Brookhaven National Laboratory, Oak Ridge National Laboratory, Lawrence Berkeley National Laboratory, Argonne National Laboratory, CERN (research collaborations), Los Alamos National Laboratory, National Institute of Standards and Technology, Rutherford Appleton Laboratory, Paul Scherrer Institute, European Synchrotron Radiation Facility, Diamond Light Source, Stanford Synchrotron Radiation Lightsource, Max Planck Institute for Solid State Research, and the Institut Laue–Langevin.

Classification and Solid Solution Series

The plagioclase series classification includes endmembers albite and anorthite and intermediate members often named oligoclase, andesine, labradorite, bytownite; these nomenclatures are adopted by bodies like the International Mineralogical Association and used in publications from the Journal of Petrology, Contributions to Mineralogy and Petrology, Nature Geoscience, Science, Geology, Earth and Planetary Science Letters, Journal of Geophysical Research, Lithos, Mineralogical Magazine, Canadian Mineralogist, American Mineralogist, Tectonics, Journal of Volcanology and Geothermal Research, Precambrian Research, Journal of Metamorphic Geology, Chemical Geology, Geochimica et Cosmochimica Acta.

Formation and Geological Occurrence

Plagioclase forms in environments ranging from mid-ocean ridges studied by the Intergovernmental Oceanographic Commission and NOAA to continental arcs like the Andes, Cascades, Aleutian Islands, Japan Arc, Iceland, Hawaiian Islands, Ethiopian Rift, East African Rift, Karoo Basin, Deccan Traps, Siberian Traps, Great Dyke (Zimbabwe), Bushveld Complex, Sierra Nevada, Rocky Mountains, Appalachians, European Alps, Himalayas, Ural Mountains, Andean Orogeny, Caledonian orogeny, Variscan orogeny, and ancient cratons such as the Kaapvaal Craton, Pilbara Craton, Canadian Shield, Yilgarn Craton, Siberian Craton.

Petrogenesis and Metamorphism

Plagioclase composition and zoning record magmatic processes in plutons examined at field sites like Mount St. Helens, Mount Etna, Mount Vesuvius, Mount Fuji, Eyjafjallajökull, Krakatoa, Santorini, Yellowstone National Park, Long Valley Caldera, Campo de Calatrava, Ischia, Campi Flegrei, Mount Pinatubo, Toba Caldera, Mt. Merapi, and are interpreted using techniques developed at centers like Scripps Institution of Oceanography, Woods Hole Oceanographic Institution, Lamont–Doherty Earth Observatory, Institut de Physique du Globe de Paris, GFZ German Research Centre for Geosciences, Australian National University Research School of Earth Sciences, CNRS, CSIC, CNR, FWO, ERC-funded projects, and with isotopic labs at PRIME lab and NERC Radiocarbon Facility.

Optical and Physical Identification

Thin-section petrography of plagioclase uses polarizing microscopes by manufacturers showcased at meetings of the Royal Microscopical Society, devices applied in labs at Natural History Museum, London, American Museum of Natural History, Field Museum, Museum für Naturkunde Berlin, National Museum of Natural History (France), Smithsonian National Museum of Natural History, Victoria and Albert Museum (collections collaborations), and imaging with SEM, TEM, and microprobe facilities at Cambridge Crystallographic Data Centre, European Microscopy Society, Microanalysis Society, Zeiss, Leica Microsystems, Hitachi, FEI Company, JEOL, Oxford Instruments, Bruker.

Economic Uses and Industrial Applications

Plagioclase-bearing rocks have economic significance for construction and dimension stone in quarries operated by firms and institutions associated with infrastructure projects by the World Bank, Asian Development Bank, European Investment Bank, United Nations Development Programme, and for mineral exploration by companies like Rio Tinto, BHP, Vale, Barrick Gold, Anglo American, Newmont Corporation, Glencore, Freeport-McMoRan, Gold Fields, ArcelorMittal, Cleveland-Cliffs, LafargeHolcim, Votorantim Group, CEMEX, HeidelbergCement, CRH plc, Sibelco, Holcim, Saint-Gobain, Caterpillar Inc., Komatsu, and research collaborations with universities and national labs for aggregate standards, ceramics, glass manufacture, and planetary analogue studies for agencies like NASA, European Space Agency, Roscosmos, China National Space Administration, Indian Space Research Organisation, JAXA, ISRO, CNES, and CSA.

Category:Minerals