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Structural Changes and Isomorphic Substitution in Illites from Limestones of Variable Degrees of Metamorphism
Author(s) -
Gavish E.,
Reynolds R. C.
Publication year - 1970
Publication title -
israel journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.908
H-Index - 54
eISSN - 1869-5868
pISSN - 0021-2148
DOI - 10.1002/ijch.197000054
Subject(s) - metamorphism , chemistry , octahedron , illite , crystallography , lattice (music) , diffraction , mineralogy , clay minerals , crystal structure , geology , geochemistry , physics , optics , acoustics
Eleven samples of illites were separated from limestones which have undergone variable degrees of metamorphism and analyzed by X‐ray diffraction to give twelve orders of the (001) reflections. The observed structure factors were calculated with a computer and compared to calculated structure factors of a hypothetical model through a process of “refinement”. The variable parameters in the process of “refinement” were: the distance of OH, Si and O from the center of the unit cell, the temperature coefficient, and the amount of K + and Fe +3 in the lattice of the unit cell. A one‐dimensional Fourier synthesis calculated the electron densities along the C axis within the unit cell. The percent 2M polymorph in the illites, as well as the oxygen isotope ratio of the limestones from which the illites were extracted, was also calculated. These two parameters were used as indicators of the degree of metamorphism of the samples collected. There is an inverse correlation between the proportion of 2M polymorphs and the O 18 /O 16 ratio. There is no clear correlation between the amount of K + in the lattice and the degree of metamorphism of the samples. There is an increase of Fe +3 substituted in the octahedral layer of the illite, with an increased degree of metamorphism of the limestones.