New insights into the mechanism for chloritization of biotite using polytype analysis
-
Toshihiro Kogure
and
Jillian F. Banfield
Abstract
Near-atomic-resolution transmission electron microscopy was used to investigate the chloritization mechanisms of biotite in a granitic rock and to reveal polytypic details of the resulting chlorite. Comparison of stacking sequences in 2M1 and longer period biotite polytypes with sequences in areas containing chlorite layers revealed that typically, two biotite layers transform to one chlorite layer, losing two potassium interlayer sheets and two tetrahedral sheets. In some cases, more than two biotite layers are replaced by one chlorite layer. Less commonly, a potassium interlayer sheet is replaced by a brucite-like sheet. One biotite layer is transformed to one serpentine layer via loss of a potassium interlayer and a tetrahedral sheet in places. Based on the relative frequency of the two chlorite layers to one biotite layer vs. one biotite layer to one chlorite layer mechanisms, the net result of chloritization is a considerable volume decrease along c*. Near-atomic-resolution images recorded down [010], [310], or [31̄0] revealed that the chlorite polytype in the biotite-chlorite interstratifications is predominantly IIbb. However mixtures of Ibb, Iab, IIab, and IIbb also occur. The “aa” stacking sequences were never found. Chlorite polytypes may be determined in part by the chloritization mechanisms and in part by relief of local shear by a/3 displacements.
© 2015 by Walter de Gruyter Berlin/Boston
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Articles in the same Issue
- Measurement of crystal size distributions
- Pressure dependence of the solubility of Ar and Kr in melts of the system SiO2-NaAlSi2O6
- Solubility behavior of water in haploandesitic melts at high pressure and high temperature
- Proton-containing defects at forsterite {010} tilt grain boundaries and stepped surfaces
- Incorporation of Fe3+ into forsterite and wadsleyite
- Molecular dynamics simulation of Al/Si-ordered plagioclase feldspar
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- The dissolution of hectorite: In-situ, real-time observations using atomic force microscopy
- Quantification of minor phases in growth kinetics experiments with powder X-ray diffraction
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- Crystal chemical variations in Li- and Fe-rich micas from Pikes Peak batholith (central Colorado)
- The crystal structure of TlAlSiO4: The role of inert pairs in exclusion of Tl from silicate minerals
- The structure of agrinierite: a Sr-containing uranyl oxide hydrate mineral
- The crystal structure of namibite, Cu(BiO)2VO4(OH), and revision of its symmetry
- The crystal structure of pararobertsite and its relationship to mitridatite
- Description and crystal structure of cabalzarite Ca(Mg,Al,Fe)2(AsO4)2(H2O,OH)2, a new mineral of the tsumcorite group
- Tegengrenite, a new, rhombohedral spinel-related Sb mineral from the Jakobsberg Fe-Mn deposit, Värmland, Sweden
