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Predicted compositions for high‐density hydrous magnesium silicates
Author(s) -
Finger L. W.,
Prewitt C. T.
Publication year - 1989
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/gl016i012p01395
Subject(s) - octahedron , magnesium , olivine , silicon , materials science , stacking , stoichiometry , tetrahedron , silicate , crystallography , mineralogy , formula unit , substructure , geology , crystal structure , chemistry , metallurgy , structural engineering , engineering , organic chemistry
Recent studies of high‐pressure hydrous magnesium silicates have revealed a wide variation of structures and chemistries. These materials are composed of layers of octahedra that have “rock‐salt” topology modified by vacancies and silicon replacing magnesium, and by layers with octahedral magnesium, tetrahedral silicon and olivine‐humite series stoichiometry. There are two ways to form a close‐packed oxygen substructure from these types of layers. One scheme has a 1∶1 ratio of the two layers and a four‐unit or 9.4Å repeat. The second stacking sequence has two olivine‐series layers for each octahedral unit and a six‐layer or 14Å repeat. A general formula for the compositions of these phases is , where mod( n ,2) is the remainder when n is divided by 2; n = 1,2,3,4, ∞; and m = 1,2, ∞. This formula has been used to predict compositions and room pressure‐temperature densities. These phases have mixed tetrahedral and octahedral coordination for silicon and could be important constituents of the mantle transition zone.