Abstract
Occurrence, optical properties, chemical composition, crystal structure and formation environments of the phillipsite within deep-sea manganese nodules were systematically investigated. Phillipsite occurs in manganese nodules as nuclei along consolidated bottom sediments, weathered volcanic debris, and interstitial grains in all layers of manganese encrustments. Phillipsite is predominantly a pseudomorph of volcanic shards, and occurs as white to pale-yellow, lath-shaped and equant crystals. They show prismatic, blocky, and bladed aggregations, 2 to 20 μm long and 2 to 5 μm thick. The chemical formula of phillipsite in a microprobe analysis is (Ca 0.1Mg 0.3Na 1.1K 1.5) (Fe 0.3Al 4.2Si 11.8)O 32 · 10H 2O indicating a relatively siliceous and alkalic composition. The Si/(Al + Fe 3+) ratio is 2.37 to 2.78, alkalis greatly exceed the divalent exchangeable cations, and the Na/K ratio is 0.59 to 0.81. The mineral is monoclinic ( P2 1 m ) with the unit-cell parameters a = 10.005 A ̊ , b = 14.129 A ̊ , c = 8.686 A ̊ , β = 124.35 °, and V = 1013.6 A ̊ 3 . Phillipsites in manganese nodules formed apparently authigenically at a temperature less than 10 °C, and they crystallized at a pressure of less than 0.7 kbar, and pH of about 8 due to deep-sea environments.
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