• Journal of the Mineralogical Society of Korea
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• v.4 no.2
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• pp.90-98
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• 1991

This study introduces a new structural model of 1M 2:1 trioctahedral clay minerals or, more generally, 2:1 trioctahedral phyllosilicates. The structural model requires only the chemical formulae of the clay minerals as an input and uses the regression relation (Radoslovich, 1962) to calculate the a- and b-dimensions of the phyllosilicates with the given chemical formulae. The atomic coordinates of the constituent atoms are geometrically calculated for C2/m space group under the assumption that the interatomic distances are constant. To determine the c-dimension, this study calculates the binding energies of 1M 2:1 trioctahedral phyllosilicates as a function of d(001) and find the minimum energy producing d(001). The structural model generates the cell dimensions, interaxial angles, interatomic distances, octahedral, tetrahedral and interlayer thickness, polyhedron deformation angles and atomic coordinates in the unit cell. The simulated structural parameters of phlogopite and annite are very close to the reported data by Hazen and Burnham (1973), suggesting that the structure simulation using only the chemical formule is successful, and thus, that the structural model of this study overcomes the difficulties in the previous models by other investigators.

• Journal of the Mineralogical Society of Korea
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• v.4 no.1
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• pp.11-21
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• 1991

XRD patterns of biedellite-nontronite and saponite-iron saponite series were investigated using one-dimensional pattern simulation method. Ethylene-glycolate smectites show stronger 002 and 003 reflections than hydrated specimens do. The intensities of the 002 and 003 reflections change systematically as a function of Fe enrichment in both types of smectites. The intensity ratio of 002/003 increases with increasing. Fe in both dioctahedral to the higher scattering factor of Fe than those of Al and Mg, and the scattering power of various smectites can be compared quantitatively by calculating the scattering factors of octahedral cations. Interlayer cations cause less effect on XRD profile than octahedral cations as Fe do. Although 001 reflections provide informations about the overall scattering power of the octahedral sheet, some ferrous dioctahedtal smectite cannot be distinguished unambiguously from trioctahedral smectites on the basis of XRD profile. Simulation showed that heterogeneous smectites exhibit 001 intensity distribution that is almost identical to that of homogeneous smectites having the average composition of heterogeneous ones. The broadening of 001 reflections may not be useful in evaluating the degree of heterogeneity of smectite unless other factors affecting the broadening are well known.

• Journal of the Mineralogical Society of Korea
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• v.30 no.4
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• pp.161-172
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• 2017

Clay minerals play a major role in the geochemical cycles of metals in the Critical Zone, the Earth surface-layer ranging from the groundwater bottom to the tree tops. Atomistic scale research of the very fine particles can help understand the fundamental mechanisms of the important geochemical processes and possibly apply to development of hybrid nanomaterials. Molecular dynamics (MD) simulations can provide atomistic level insights into the crystal structures of clay minerals and the chemical reactivity. Classical MD simulations use a force field which is a parameter set of interatomic pair potentials. The ClayFF force field has been widely used in the MD simulations of dioctahedral clay minerals as the force field was developed mainly based on dioctahedral phyllosilicates. The ClayFF is often used also for trioctahedral mineral simulations, but disagreement exits in selection of the interatomic potential parameters, particularly for Mg atom-types of the octahedral sheet. In this study, MD simulations were performed for trioctahedral clay minerals such as brucite, lizardite, and talc, to test how the two different Mg atom types (i.e., 'mgo' or 'mgh') affect the simulation results. The structural parameters such as lattice parameters and interatomic distances were relatively insensitive to the choice of the parameter, but the vibrational power spectra of hydroxyls were more sensitive to the choice of the parameter particularly for lizardite.

• Journal of the Mineralogical Society of Korea
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• v.27 no.4
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• pp.271-281
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• 2014

The physicochemical properties of clay minerals have been investigated at the atomistic to nano scale. The microscopic studies are often challenging to perform by using experimental approaches alone. In particular, hydroxyl groups of octahedral sheets in 2:1 clay minerals have been hypothesized to impact the sorption process of metal cations; however, X-ray based techniques alone, a common tool for mineral structure examination, cannot properly test the hypothesis. The current study has examined whether computational mineralogy techniques can be applied to examine the hydroxyl structures of clay minerals. Based on quantum-mechanics and molecular-mechanics computational methods, geometry optimizations were carried out for representative dioctahedral and trioctahedral phyllosilicate minerals. Both methods well reproduced the experimental lattice parameters; however, for structural distortion occurring in the tetrahedral or octahedral sheets, molecular mechanics showed significant deviations from experimental data. The orientation angle of the hydroxyl with respect to (001) basal plane is determined by the balance of repulsion between the hydroxyl proton and Si cations of tetrahedral sites; the quantum-mechanics method predicted $25-26^{\circ}$ for the angle, whereas the angle predicted by the molecular-mechanics method was much higher by $10^{\circ}$ (i.e., $35^{\circ}$). These results demonstrate that computational mineralogy techniques are a reliable tool for clay mineral studies and can be used to further elucidate the roles of hydroxyls in metal sorption process.

• Journal of the Mineralogical Society of Korea
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• v.13 no.4
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• pp.196-204
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• 2000

We present characteristics of hydrothermal chlorite and its interstratification with 7-$\AA$ mineral phase that occur in the propylitic alteration zone of the Bobae sericite deposit formed in rhyodacitic tuff. Chlorite is found as disseminated fine-grained aggregate or replacement materials of precursor minerals such as Fe-oxides and amphibole. Based on X-ray diffraction(XRD), all chlorites belong to IIb polytype and the (060) reflections averaging $1.53~1.54\AA$ indicate a trioctahedral structure. Chemical compositions of chlorite show that the Fe/(Fe+Mg) values are mostly in the range of 0.44~0.53, and cation deficiencies in octahedral sites range from 0.06 to 0.37. Under scanning electron microscope(SEM) chlorite occurs as well-crystallized aggregates and is subparallely stacked in interstices or between grain boundaries of associated minerals. transmission electron microscopic(TEM) images reveal that chlorite shows regular layers with $14-\AA$ spacings, locally interstratified with $7-\AA$ or $21-\AA$ periodicities. The $21- \AA$ periodicity corresponds to the sum of the $d_{001}$ values of chlorite and $7-\AA$ phase. The chlorite packet coexisting with 7-$\AA$ layers displays abundant defects such as edge dislocations and layer terminations. Selected-area electron diffraction(SAED) indicates that chlorite and $7-\AA$ phase are randomly interstratified in the mixed-layer areas. We propose a lateral change of layers for the polymorphic transition of $7-\AA$ phase to chlorite.e.

• Journal of the Mineralogical Society of Korea
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• v.11 no.1
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• pp.45-67
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• 1998

FORTRAN program PHYLS was developed to model the structures of 2:1 1M and 2M1 phyllosilicates on the basis of geometrical analyses. Input to PHYLS requires the chemical composition and d(001) spacing of the mineral. The output from PHYLS consists of the coordinates of the crystallographically independent sites in the unit cell, and such structural parameters as the cell dimensions, interaxial angle, cell volume, interatomic distances, and deformation angles of the polyhedra. PHYLS can generate these structural details according to the user's choice of space group and cation configuration. User can choose one of such space groups as C2/m, C2,and C2/c and such cation configurations as random and ordered tetrachedral/octahedral cation configurations. PHYLS simulated the structures of dioctahedral and trioctahedral phyllosilicates having random tetrahedral cation configuration fairly close to the reported experimentally determined structures. In contrast, the simulated structures for ordered tetrahedral cation configurations showed greater deviation from the experimentally determined structures than those for random configurations. However, if the cations were partially ordered and the sizes of the tetrahedra became similar, the simulated PHYLS may be helpful in various investigations on the relationships between structures and physicochemical properties of the phyllosilicates.

• 한국해양학회지
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• v.26 no.4
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• pp.313-323
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• 1991

Fine-grained sediments of the Han River and adjacent Kyonggi Bay have been studied using the powder x-ray diffractometer in order to study the distributional characteristics of clay minerals in the bottom and suspended sediments. The result of the XRD analyse shows that the major clay minerals in the lower Han River are composed of illite (57.1%), kaolinite (22.9%), and chlorite (19.6%) and that those of the Han River Estuary are composed of illite (67.2%), chlorite (16.5%), kaolinite 915.5%), and smectite (1.3%). The variation of mineral content shows distinct distributional characteristics depending on sedimentary environments. The illite content increases gradually approaching the Kyonggi Bay and kaolinite content decreases toward the sea within the range between 11% and 23%. The trend of chlorite is similar to that of kaolinite, the amount of which ranges between 14% and 19%. Smectite content is lower than 3%. Analysis of illite using peak-intensity ratio (001/002) indicates that two types of illites occur in the study area. Dioctahedral-type illite occurs as an indicator of the marine sediments. The illites distributed between the Kyonggi Bay and the Han River are mixtures of dioctahedral- and trioctahedral-types. This study indicates that the distribution of illite, kaolimite, and chlorite has been influenced mainly by the supply from the Han River and redistributed by estuarine circulation, such as tidal circulation and seasonal variation of river discharge. However, smectite is apparently supplied from other sources such as Yellow Sea or China. This study suggests that estuarine mixing system and seasonal variations of river discharge are the major factors controlling the distribution pattern of clay minerals in the study area.

• Journal of the Mineralogical Society of Korea
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• v.16 no.3
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• pp.215-222
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• 2003

The Rietveld structure refinement for the natural trioctahedral mica, phlogopite-1M (Parker Mine, Quebec, Canada) has been done by high resolution neutron powder diffraction at $25^{\circ}C$ and -263$^{\circ}C$. The structural formula of phlogopite determined by electron probe microanalysis is $K_2$(M $g_{4.46}$F $e_{0.83}$A $l_{0.34}$ $Ti_{0.22}$)(S $i_{5.51}$A $l_{2.49}$) $O_{20}$(O $H_{3.59}$ $F_{0.41}$). Cell parameters are a=5.30∼5.31 $\AA$, b=9.18∼9.20 $\AA$, c=10.18∼10.21 $\AA$, $\beta$=100.06∼100.08$^{\circ}$. Refinements converged to R values in the range of $R_{p}$=2.35%, $R_{wp}$=3.01%, respectively. In this study, the OH bond length is calculated to 0.93 $\AA$ at room temperature and 1.03 $\AA$ at -263$^{\circ}C$, and the angles between OH vector and (001) plane are obtained 93.4$^{\circ}$∼93.6$^{\circ}$. The decrease in the length of OH with the increase in temperature should be due to the hydrogen bonding in the structure of phogopite.e.e.f phogopite.e.e.

• Journal of the Mineralogical Society of Korea
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• v.28 no.2
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• pp.127-133
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• 2015

Li-bearing muscovite is commonly found along with trioctahedral lepidolite in granitic pegmatites. Structurally, $Li^+$ ions can replace $K^+$ ions in the interlayer (Int) of muscovite or incorporate into vacancies of the dioctahedral sheet (Sub). However, detailed mechanism of the lithium incorporation into muscovite is challenging to investigate using experimental techniques alone. In the current study, density functional theory (DFT) has been applied to examine the crystal structure and energy variation when $Li^+$ resides in the interlayer or the octahedral sheet. Depending on the position of $Li^+$ (i.e., Int vs. Sub), DFT showed significant differences in the mica's structures such as lattice parameters, sheet thickness, interlayer separation, and OH angles with respect to the ab plane. DFT further showed that, in pure muscovite, $Li^+$ has a lower energy when it is located in Int than Sub. By contrast, in the case of $Fe^{2+}$ substitution into the octahedral sheet, $Li^+$ has a lower energy in Sub than in Int. These results imply that $Li^+$ incorporates into the Al octahedral sheets only when the octahedral sheets possess structural charges, suggesting cation substitution in the octahedral sheets plays an important role in the Li incorporation mechanism into muscovite. They can also explain the experimental observation about the positive relationship between $Fe^{2+}$ and $Li^+$ amounts in Li-bearing muscovite.

• Journal of the Mineralogical Society of Korea
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• v.29 no.3
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• pp.103-111
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• 2016

Li-bearing hectorite, one member of trioctahedral smectite, occurred large in quantity and confirmed in Turkey western sedimentary boron deposit. Li-bearing hectorite attracted a particular attention because it is one of potential lithium resources. There have been no consensus for the change of hectorite due to heat and acid treatment although it is very important to use in industrial application. In this study, we examined changes of hectorite after heat and acid treatment as well as acid treatement followed by heating. We used clay ores collected in Bigadic deposit, which contained the highest $Li_2O$ content in Turkey boron deposits. Hectorite showed a strong endothermic reaction at $84^{\circ}C$ due to dehydration of absorbed water and interlayer water and a weak endothermic reaction above $600^{\circ}C$ owing to dehydration of crystallization water. The first endothermic reaction accompanied a large weight loss about 6%. Hectorite decomposed into enstatite, cristobalite and amorphous Fe material at $762^{\circ}C$ with exothermic reaction. When hectorite reacted with 3 kinds of 0.1 M acid during 1 hours, it had a good dissolution efficiency with $H_2SO_4{\geq}HCl$ > $HNO_3$ in order.