The brownstone facies was proposed by Cann (1979) as a low-temperature mineral facies encompassing ocean-floor weathering and cool hydrothermal alteration on the ocean floor. The most widespread secondary minerals under oxidizing conditions include a K-rich dioctahedral Fe-illite resembling celadonite. This replaces olivine, occupies vesicles, replaces interstitial glass, and may eventually replace augite. Under reducing conditions, its place is taken by saponite, and pyrite is also characteristic. Plagioclase may be replaced by clay minerals or potassium feldspar. Glassy rinds of basaltic pillow lava alter to palagonite in association with phillipsite and other low-temperature zeolites and calcium carbonate.
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Bibliography
Cann, J. R., 1979, Metamorphism in the ocean crust, in M. Talwani, C. G. Harrison, and D. E. Hayes, eds., Deep Drilling Results in the Atlantic Ocean: Oceanic Crust. Washington: American Geophysical Union, 230–238.
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© 1989 Van Nostrand Reinhold
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Coombs, D.S. (1989). Brownstone facies . In: Petrology. Encyclopedia of Earth Science. Springer, Boston, MA. https://doi.org/10.1007/0-387-30845-8_29
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DOI: https://doi.org/10.1007/0-387-30845-8_29
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