• Journal of the Mineralogical Society of Korea
• /
• v.3 no.1
• /
• pp.34-43
• /
• 1990

Crystal-chemical study of hexagonal 7$\AA$ phyllomanganate minerals reveals that they have hexagonal layer structures with variable c dimensions which depend on the nature of interlayer cations and content of water molecules between edge-sharing [MnO6] octahedral layers. Approximately one out of nine octahedral sites is statistically vacant, leading to the general unit cell formula R2xMn4+1-xO2.nH2O, where R=Ca, Mn2+, Mg, K, Na;x=0.09-0.14 ; n-0.37-0.84. Z=1. The minerals of this formula fall under the name of rancieite group. It includes Ca-diminant (rancieite), Mn2+-dominant (takanelite), Na-dominant (birnessite), and Mg-dominant members. Minerals of the rancieite group occur predominantly in two different hydration states, i.e., n shows the values around 0.35 and 0.75. It is suggested that minerals of higher hydration state be called as species(i.e., rancieite, etc.) and those of lower hydration state be called as dehydrated varieties(i.e., dehydrated rancieite,etc.).

• Journal of the Mineralogical Society of Korea
• /
• v.10 no.2
• /
• pp.82-96
• /
• 1997

Buserties are known to have layer structures with variable C dimension which depended on the nature interlayer catious and contents of water molecular between edge-sharing [MnO6] octabedral layers. Na-, Ca-, Mg-, and Zn-buserties were synthesized in the laboratory and studied for to know the structural states of water molecules and the role of catious in the buserite structures. With lowering the relative humidity(RH), Ca-buserite begins to dehydrate at 27% RH and proceeds further very slowly. Mg- and Zn- buserite also slow dehydration above 2% RH. With gradual ineveasing temperature Ca- and Zn-buserite show abrupt shifting of 10$\AA$ peak (10$\AA$-phare) toward 7$\AA$ peak. All of 7$\AA$-phare are further dehydrated to 5$\AA$-phare by further increasing temperature. It suggests that interlayer catious play a crucial role in the dehydration behavious of buserites. Simulation of one-dimensional X-ray diffraction patterns of buserties show that buserites have three layers of water molecules of different types: the very loosely bound and tightly bend waters, instead of two layers that was regarded by previous authers. The very loosely bound water is sited I open space of the interlayer, the loosely bound water is bound on the tightly bound water by hydrogen bond, and the tightly bond water in coodinately bound on the interlayer catious.

• Journal of the Mineralogical Society of Korea
• /
• v.16 no.4
• /
• pp.333-339
• /
• 2003

A new mineral, Zn analogue of rancieite (Chimooite), has been discovered at the Dongnam mine, Korea. It occurs as compact subparallel fine­grained flaky or acicular aggregates in the massive manganese oxide ores which were formed by supergene oxidation of rhodochrosite­sulfide ores in the hydrothermal veins trending NS­N25E and cutting the Pungchon limestone of the Cambrian age. The flakes of chimooite are 0.2 mm for the largest one, but usually less than 0.05 mm. The acicular crystals are elongated parallel to and flattened on (001). This mineral shows gradation to rancieite constituting its marginal part, thus both minerals are found in one and the same flake. Color is bluish black, with dull luster and brown streak in globular or massive aggregates. Cleavage is perfect in one direction. The hardness ranges from 2.5 to 4. Under reflected light it is anisotropic and bireflectant. It shows reddish brown internal reflection. Chemical analyses of different parts of both minerals suggest that rancieite and chimooite constitute a continuous solid solution series by cationic substitution. The empirical chemical formula for chimooite has been calculated following the general formula, $R_2_{x}$ M $n^{4+}$$_{9­x}$ $O_{18}$ $.$n$H_2O$ for the 7 $\AA$ phyllomanganate minerals, where x varies from 0.81 to 1.28 in so far studied samples, thus averaging to 1.0. Therefore, the formula of Zn­rancieite is close to the well­known strochiometric formula $_Mn_4^{4+}$ $O_{9}$ $.$4$H_2O$. The mineral has the formula (Z $n_{0.78}$N $a_{0.15}$C $a_{0.08}$M $g_{0.01}$ $K_{0.01}$)(M $n^{4+}$$_{3.98}$F $e^{3+}$$_{0.02}$)$_{4.00}$ $O_{9}$ $.$3.85$H_2O$, thus the ideal formula is (Zn,Ca)M $n^{4+}$$_4$ $O_{9}$ $.$3.85$H_2O$. The mineral has a hexagonal unit ceil with a=2.840 $\AA$ c=7.486 $\AA$ and a : c = 1 : 2.636. The DTA curve shows endothermic peaks at 65, 180, 690 and 102$0^{\circ}C$. The IR absorption spectrum shows absorption bands at 445, 500, 1630 and 3400 c $m^{1}$. The mineral name Chimooite has been named in honour of late Prof, Chi Moo Son of Seoul National University.ity.versity.ity.y.

• Korean Journal of Mineralogy and Petrology
• /
• v.33 no.1
• /
• pp.19-28
• /
• 2020

Ranciéte is a hexagonal phyllomanganate mineral containing random Mn(IV) vacancies with hydrated Ca²⁺ cations charged balanced as interlayer cations. Its Mn²⁺ analogue is called takanelite, and ranciéite and takanelite are regarded as end-members of a solid solution series of (Ca²⁺,Mn²⁺)Mn₄O₉·nH₂O. Because the minerals are found as very small particles associated with other minerals, the crystal structures of the solid solution series have yet to be defined. In this research, we conducted classical molecular dynamics (MD) simulations of ranciéite and takanelite by varying the Mn²⁺/Ca²⁺ interlayer cation ratio to find relations between the interlayer cations and mineral structures. MD simulation results of chalcophanite group minerals are compared with experimental results to verify our method applied. Then, lattice parameters of ranciéite and takanelite models are presented along with detailed interlayer structures as to the distribution and coordination of cations and water molecules. This study shows the potentials of MD simulations in entangling complicated phyllomanganates structures.